That depends, really.
Generally speaking, though - Roth IRAs are THE PLACE for Stock-Market/Mutual-Fund investing. All the off the wall (or, not so off the wall) things like Real Estate investments, or buying up gold, or whatever other ideas you hear from people - they may be good or bad or whatnot. But your Roth IRA is maybe not the best place for that sort of thing.
The whole philosophy behind IRAs is to deliberately set aside money for the future. Anything reasonable will work for this. Explore interesting investment ideas with today's money, not tomorrow's money.
That being said - at your age I would go for the riskier options within what's available.
If I were in your situation (and I have been, recently), I would lean toward low-fee mutual funds classified as "Growth" funds.
My own personal opinion (THIS IS NOT ADVICE) is that Small Cap International funds are the place to be for young folks. That's a generalized opinion based on my feel for the world, but I don't think I'm personally competent to start making specific stock picks. So, mutual funds makes sense to me in that I can select the fund that generally aligns with my sense of things, and assume that their managers will make reasonably sound decisions within that framework. Of course that assumption has to be backed up with reputation of the specific MF company and the comparative performance of the fund relative to other funds in the same sector.
As to the generalized question (how else can you work toward financial stability and independence), outside of your Roth IRA: find ways to boost your earning potential over time, and buy a house before the next bubble (within the next 18 months, I'm GUESSING).