Go slow, be patient, in every aspect!
You will find a lot of advice here and in the "sticky" (always listed first) posts under each of the sub-forums.
Here's the things I wish people had told me before hand:
1.
cycling with fish-in is not crazy, and it can be much easier than a
fish-less cycle. it is worth considering, both have benefits and drawbacks. DYOR
2.
don't rush to stock your tank.
watch tons of videos. learn about behaviors and interactions between species. aim to understock.
when you go to the aquatic pet store to shop, look at the fish in every single tank and try to spot
diseases and injuries. if any of the tanks have visible problems, consider shopping elsewhere because any "ok" looking fish in the tanks you're browsing could very well be hiding problems that will emerge when you bring them home.
Sometimes the store is very busy and the human helpers will be stressed, this stress can be transferred to your new fish in the bagging process, setting you up for failure before they even get home! Aim to shop at low traffic times so you can take your time as well as the staff. be willing to walk home empty handed if it is not feeling just right and meeting your stocking goals. don't change the stocking plan because your significant other came with and was struck by a case of the "oohs and ahhs".