With no credit cards or other open accounts, you have limited ways of improving your score. You have to have credit and show that you can handle it for the scores to go up.
If you now have a good history of utility payments, then Experian Boost could help you (www.experian.com/boost), but that only helps you if find creditors that only look at Experian. If the Boost works to improve your score at Experian, you could theoretically also freeze Equifax and TransUnion and see if new creditors will approve you only based upon the Experian credit score.
