The results will obviously be much more pronounced than getting better at something you have already somewhat mastered. Attempt greater levels of what you are already good at. Another tact to take would be to stretch yourself in an area that you already have some skill and ability in. That is O.K., but needs to fit in with your overall goals. Commit time each day to improvement.
Steady improvement is the way to go.
In fact, you may not see improvement for days or weeks. You may feel like you are failing each time. But alas, eventually you will get it and your skill will increase to the next level. The key is day in, day out, spending time working on improving. Even five minutes a day equals a half hour a week, two hours a month.