well I guess I would start at the first thing. what lane do you main? who do you main that lane with? from there you can get into ok what are my strengths what are my weaknesses regarding champion match ups/counters.
I would watch youtube videos on how to manage someone who's counterpicked you. look at where people ward and how often they do it. look at how they CS and dont just look at how your champion CS but how your opponents do. You'll notice patterns on when they are about to go in on you. also keep in mind your positioning, from level 3 to 6 I will push the lane up but not stick around in the middle of the lane since you really wont do too much damage to the turret anyways; generally junglers will look for early ganks around that time as well so leaving yourself to far up in a lane will leave you susceptible if your champ doesnt have natural escapes or youve wasted flash.
another thing is map awareness which goes along with warding. if you're teammates arent warding tell them, 'please ward everyone'. if they dont just play defensively as to not get caught out. wards are extremely important.
I guess the checklist to focus improving is (1) positioning and CS (2) map awareness/warding (3) champion skills/counters, by this I mean truly getting to know the limits and ranges of your champions skills and abilities (4) item and Rune builds; which can be tied in with (3) and lastly one of the most important is (5) communication, learn to communicate with people through pings this will tie in just about all the above. communicating helps others with map awareness, helps set up ganks and early kills, helps with objective control and many other things.