Hate to say it, but the answer is probably "wait". If you have low 700s, I'd guess you have 0 to 2 delinquent payments in your credit history, and if you do, they're old. You also aren't having any financial problems currently. So that leaves you to just wait on 3 things to slowly happen.
1. If you do have an old delinquent payment on there, it'll probably drop off soon. You can find the number of years that different types of credit marks stay on your report online pretty easily, if you're interested.
2. Your average credit age will increase. Every line of credit (mortgage, credit card, loans, etc.) you have has an age, and the credit bureaus average those ages as part of your score. So if you opened a credit card 3 years ago and got 2 student loans 5 years ago (and you're still paying them off), your average is (3+5+5)/3=4.3 years. You probably have more than that going on, but the point is, as time goes on, the accounts get older, your average goes up, and your score goes with it. Credit cards are great for this because they just keep getting older, unlike a loan, which will get paid off and then vanish from your average.
3. Your debt-to-income ratio will increase. Over time you'll probably start making more money. Simultaneously, any loans you have will get smaller and smaller. More income and less debt = better ratio. Score goes up.
So yeah, just keep up good practices, live within your means, and don't miss payments. The score will take care of itself. When I got out of college, I had a 620. I didn't do anything spectacular after that. I just made payments on time, only had 2 credit cards, bought a house and am paying that loan, bought some cars and paid/paying those loans, blah blah. Now, 9 years later, without paying any special attention to my credit score, I have an 817.
