Hello and welcome,
With a 10g tank you are some what restricted to what you can put in the tank. I would think a Green Chromis, a yellow clown goby, maybe a Blennie, Cleaner shrimp , sixline Wrasse, neon Goby, yellow Watchman Goby, maybe a Firefish Goby, green clown goby. ( these for the most part should be fine with your clown fish and each other )
Now... I'm not saying all of these will fit in your tank, but to add 1 or 2 more and say a cleaner shrimp should be fine. I would defenately not go more than 3 total. Don't add them all at once either. Add 1 ( unless you are getting a pair ) then give it a couple of weeks before you add another.
Other Canreef members will most likely have different opinions, but thats whats great about this site. This is just my 2 cents worth.
Enjoy your new Hobby and again Welcome.
CHEERS