The ideal thing to do is to decide your entire stocking before you get the first fish, then add in order, with the shyest/least territorial fish first.
Good first fish include most tank-bred fish, gobies, clowns, chromis.
I'm assuming you've already added your cleanup crew. If not, start with the snails and crabs, etc. eTropicals.com has a nice build-your-own package where you get free shipping if you spend over $60. If yours is a nano tank, that probably won't be practical.