Play 1v1 with someone at your skill level. See how long it takes for the match to end, after a month, test that again, If its faster, that means you are better, If it takes about the same amount of time, but there were more kills in that time frame (IE lets say you got 10 kills the first time, and 20 kills the next), then it is still signs of improvement, just keep up the hard work.
I got damn good at plasma grenades in Halo CE when I went to a friends house and played Halo 2 for the first time (I had only played video games twice before that for about 15 minutes total). He was an asshole an stayed in a Warthog and just ran me over constantly. I became obsessed with being able to stick things. Now, since then, I have lost a lot of my ability to stick players at a distance, but I have maintained my ability to destroy vehicles. So in short, find something to drive for, train yourself in a specialty that you see yourself encountering a considerable amount.
Good Luck