I would suggest investing reading time in all the "stickies" (posts at the top of the forum) in each area for tank size, water change needs, general care, etc.
I'm relatively new, but if I had it to do over again, I would have skipped buying the one gallon and 2.5 gal tanks and gone straight to the 10 gal I have now. (Much of that is because we're a busy family and the water change schedule for a 10 works much better for us.) Many people on the forum have much less than ten, but are very successful because they pay attention to the requirements of a smaller tank.
In my experience as a newbie, tank size, water changes, types of plants (natural or silk, and be careful, not all silk are safe) and decor, type of filter (after many other dealings, I chose sponge), basic info on diseases, best type of food, etc, and basic info on how to choose a healthy betta are the areas where the time I've invested in learning has brought the biggest payoff. The amount of information here is a bit overwhelming, but with some reading you can go into it as a much more knowledgeable newbie than I was. (You can probably save A LOT of money as well...I did everything backwards...LOL!)
Be aware of beginning to look at fish in the store. I fell in love with the fish first and thus came home with all the wrong stuff and slowly had to piece together what to do. Glad my guy had a strong constitution, or I'd have killed him for sure!