Any advice for a support: always falliing behind in level, in goog game

In lane you want to keep on par with your ADC in terms of levels. To keep up, try to stay in the EXP range. It's also a good thumb rule so that both of you can save each other.

After lane, rotate in between scouting sessions, and "leeching" sessions. Try to keep that thumb rule as you scout as well.

At first it could get tedious, but with enough practice it kinda becomes muscle memory. A good guideline is basically the width of your screen when it's locked.