Regarding one's belief and faith, it recently occurred to me that at the philosophical level the choices are twofold: you either are (1) a devout and consistent Atheist - a materialist that considers that nothing exists apart from the matter and energy of the physical universe, or (2) in the most basic manner, accept that an immaterial, spiritual (even divine) reality exists that transcends the material universe. Since many don't want to place themselves firmly under the "Atheist" label, they fall into the "faith" category - willingly accepting that something may exist or be true that cannot be proven through experimentation with matter and energy.
Now if you fall under the "faith" camp, then the options become (again) twofold: to (A) adopt an established faith previously attested in history, which has likely organized itself into a codified believe system (typically represented by an organization as well), or (B) invent your own beliefs that will secure for you (i) positive interaction with the transcendent now (i.e. God, "gods," spirits, etc.) , (ii) a moral code satisfactory to those transcendent forces and works well in the world as it operates, and (iii) a favorable afterlife when the present existence transitions to it at the end of the body's life cycle. When I encounter people desirous to invent their own "religion," I encourage them that the belief system they develop really needs to meet the above criteria, and do it well enough to convince themselves they've arrived at something better than anything previous attested or practiced in history. They'll need to be confident that they're more spiritually attuned, theologically insightful and sensitive to the transcendent than any who have come before. They will need to feel a high degree of certitude regarding the afterlife and how one can be assured a pleasing one. It will help if they have the testimony of a credible witness who has been there and come back to describe it, and how one's "place at the table" is reserved.
If you're not a devout and consistent Atheist, and you eschew an established religion, then the religion you invent for yourself needs to have a way of including others, since it's unlikely you'll enjoy yours much in isolation. After all, how does one expect to relate well to a spouse that you cannot share at least some religious conversation with? Nevertheless, even if one doesn't share their religion with their spouse, the inevitability of our communal nature compels us to seek a group (or form one) in which people of like minds on a matter can gather to affirm pursuit of the common belief. Encouragement is a universal necessity, so people naturally "congregate" to encourage one another to pursue the common cause. All religions, whether attested since ancient times or recently invented mere years ago, develop followers (plural).
Your new religion will likely develop some type of natural hierarchy. Yes, I know, why the need for hierarchical structures? Isn't that the "organized religion" you're trying to escape anyway by inventing your own? Good question. But what will you do if, after a group begins to collect, an attendee seeks to persuade others in the group to think differently than you or in some manner inconsistent with your new belief patterns? Yes, even if the group gathers to affirm that each member has their own beliefs and that none can be the same, inevitably there is bound to eventually enter that one ornery person that loves to debate and hope to win others over to believing like him. Who will be the one to enforce the integrity of the group? Who will say to that person, "Look. Believe as you want, but you can't come here and spend the time upsetting others like that. Either tone it down or you'll have to leave." Who is entrusted with that kind of voice? that kind of (dare I say it) authority? *cringe*
Ok. Let's ask something else. This new religion of yours... is it all in your head, or does it interact with stuff such as symbols, talisman's, charms or fetishes? Does is have any spatial or geographical specificity? Does it involve accessing the vibes emanating from a mountain or field? Will you utilize a structure, a house or a meadow to facilitate your religious practice? ALL religions wind up developing SOME type of praxis. It's a natural human instinct. Don't worry about the money. Your basement could suffice, or you could build an ornate building. It's up to you. It is YOUR religion, after all.
What about times and seasons? Humans have historically regarded time as their most precious possession. It's a non-renewable resource that is heading toward total depletion. Therefore, religions have typically gravitated toward specific times and seasons when their practices were most effective at interacting with spiritual forces, or at least different times and seasons resulted in different nuanced interactions with the divine throughout the day, week and year; yours will be no exception. Whether it be the summer solstice, the winter solstice, a specific day in spring or a moveable date in fall, "high" days naturally will occur as the followers of your system believe they're having particularly meaningful experiences on those days. Oh, and by the way, is this religion more a daytime system or nocturnal system? Yes, I'm serious. You need to think about this. Do the spiritual realities you want to interact with seem to respond better in the dark or in broad daylight? No, it's not dependent upon whether you're a "night owl" or a "morning person."
What procedures or protocols will you invent to prepare adherents of your new religion for interacting with the divine or the spiritual? We all go through our little "rituals" of some type to "get our head in the game" concerning an important activity. Whether you're getting ready for work, going through security at the airport or respectfully witnessing the changing of the guard at the Tomb of the Unknown Soldier, we all interact with rituals here and there that convey the gravity of the occasion, adhere to protocols of approaching authority and get us in our right mind for participating. So what "rites" will you introduce in order to prepare your own mind, facilitate others with you doing the same, and invoking the presence of God, the gods or the spirits for your benefit? Will you standardize this set of "rites" so that others that believe as you do follow them to have the same effect that you do also? Will you right them down? What will THAT book be titled? Who can perform these rites for optimal effect? Anyone? Designated people? Is the designation gender specific? Many religions of the world have long standing reasons for why one is sex is preferred over the other in the context of religious rites? What would yours be?
Ok. We've covered the potential sacred times, sacred space, sacred offices, sacred objects and sacred rites of your new religion. What about a sacred text? Do you plan to codify into writing this belief system you're inventing? What will be the literary genre of this writing? Will it have one or many genres? Are you the sole author, or will you welcome the contributions of like-minded people? If a multi-author work, how will you ensure message continuity? Will you reserve full editorial authority to yourself? By what rationale do you claim such authority? Yes, I know, it's YOUR religion, but remember that it's bound to gain a following if you're serious about this. Will this "sacred text" contain poetry, history, myth, correspondence from you to like-minded people in another city? Does your religion attempt any predictions about the future? Does it express those predictions symbolically or with a high degree of detail? Do you include your rites in the sacred text, or are they contained in a separate companion volume? To what degree must your group of like-minded followers consider this sacred text "authoritative?" What I mean is, do they HAVE to believe, behave and practice according to what is written, or can they pick and choose according to personal preference? Just how "sacred" is this sacred text anyway?
Whew! That's a lot to think about. I don't mean to overwhelm you, but if you're going to invent your own religion, there's a lot to consider. I mean...if indeed you're really serious about this. Some may say that they have their "personal belief system" and "don't like organized religion" merely as a way of avoiding accountability and throwing a spiritual tantrum like some teen that refuses to grow up, but I don't think that's what you're doing. When you say that you have your "personal beliefs," I take you seriously and assume that you want to conscientiously approach the categories of religion we've considered above. If you're going to invent your own religion, there's a lot of work ahead. I don't envy you.
By contrast, I took the comparatively lazy route of simply being a Christian, and belong within that historic stream of Faith. Because I am a Christian, I derive comfort from finding my place in that "tribe," trusting those before me in history regarding the categories discussed here. Does it call for mindless adherence? Far from it, for each generation has to evaluate the extent to which tradition aligns with prescriptions and prohibitions of the sacred text (i.e. The Bible). Since I'm a Christian, the aspects of religion that you will have to invent are all pretty much invented for me already and are well attested in history. I suppose you could decide to take the "easy route" as I have, but I know you're committed to inventing your own religion.
You've sure got your work cut out for you.
Good luck with that.