Just the fact that you want to be the best you can be as a pilot will make you improve. There are so many pilot out there that have not moved on very far from the day they had their test flight.
Always try to make the plane do what you want it to, do not just accept what you end up with. You should always be flying at the altitude you have set yourself at the airspeed you have planned. When climbing, work on keeping you airspeed close to your target, when descending target your airspeed and rate of decent, when levelling off work hard at maintaining the new level and develop the ability to remain on heading and in balance. Keep your radio calls to a minimum, use your eyes and ears and situational awareness to fly safely. The occasional flight with an instructor you trust and get on with is a small cost and will also help a lot. And I do believe that the less time you have between flights the better you will become.