Pigs,
Some great ideas already in this thread, particularly about flying early to avoid turbulence ... or late in the evenings should do the same thing ... avoiding stress in your schedule etc.
Another point .. how often are you flying? If only once a week or less, it can be difficult to stay "in the groove" both physically and mentally ... which applies to almost any activity.
Along the same lines, how often are you thinking / rehearsing your flying? ... If only a few minutes worth on your to your lesson while driving in your car, that could be another major reason for lack of "knowledge retention"
.
Using a flight simulator IMO, is an interesting and fun way to stay at least mentally current, and will help somewhat with the physical skills as well.
For circuits, it's a good way to learn by repetition, the landing checklists and procedures until you probably won't even have to think about them (too much) in the real plane.
Mike