Oh my oh my. The big question. Lots of new players do whatever they can; begging much higher level peeps to group with them and then basically do their qwests for them, begging credits, buffs, armor, etc from higher level peeps only to find that they are suddenly level 90 and now their bored!! ROFL. You know it took me about 2 years to level one of my peeps up to 90, and a year for another, and i am still working on 2 others. And i've been playing the game for almost 5 years now. Here's the deal.
I bet you are not an "ACE" yet in space, so work on your space stuff. And there are all kinds of little side qwests to do. While you do not need the XP anymore many times the rewards in loot and credits are great, plus you might be able to add to your "collection" stuff. And if your on a higher population server there are always peeps looking for help in group stuff. And of course there is PVP. The only way to find some of these is first to look through this web site and others like it that might point out some little odd ball qwests you overlooked. Or just go exploring and talk to EVERYONE, NPC and peep alike, to find these. And while you're doing that you will likely find someone looking for help with a qwest or a group needing your speciality. As a Commando you will always be in high demand for lots of group stuff. I myself like the solo stuff more than the group missions and PVP, so it can get a little stale sometimes looking for missions/qwests. But i always manage to find something fun to do.
Also start another peep. You can have 2 per server, and 8 total per account. Get to work on another. And if you choose another profession you will get to do SOME different qwests/missions, although the many are the same. When you get to level 90 it is up to you to make things happen. And it is up to you to find your enjoyment. If you don't enjoy the game anymore when the obvious missions/qwests seem to dry up you most likely wont enjoy ANY MMORPG because they all have the same rules when you have maxed your level. So relax, have fun, and enjoy the Star Wars world and do whatever the heck it is you want to in the game! Being a level 90 can be very liberating and allow you to do/finish things you couldn't before. Take care my friend and remember, HAVE FUN!!