I don't think I'm gonna be helpful but I'll try anyway:
1 - ADC - Try playing champions that you're having a hard time against so you can better counter them.
2 - Mid - Rush Deathfire Grasp first, try to poke a little bit before going all in.
3 - SP - I'm not sure how you're having problems with warding placements when it's just a matter of putting them down. Please give a little bit more details.
I'm in gold 3, so here is my take on their advice:
1-Learn multiple ADC. You basically want to have your main, and two or three other ADCs you can play that counter whatever they choose. If they go cait? Learn to play tristana and get her to the late game. sound advice above.
2- I usually go dorans ring... then after I get enough for another one, I will grab one or two more depending on how far ahead I am. 2 or 3 dorans rings should put you at the point where you hit like a truck, and then you need to either build Deathfire Grasp on Ahri, or you need to build something like abyss or chalice for the MR. Depends on if you are winning or losing lane at that point.
3- Make sure you take the mastery that lets you place trinkets farther. If you start on purple/red side up top, then you can easily go into dragon pit and throw that ward over the wall into the tri bush. If you are placing wards down, and want to be safe, remember that you can actually drop a ward on a piece of terrain to get it farther than you normally would. If you add me in game, I will gladly show you how this works. You want to try and always have at least one ward:
Blue side- in tri bush.
Purple/Red side- along the corner, closer to dragon pit entrance.
This ensures that if you are watching map like you should be, that you will be able to avoid most jungle ganks. At least in this level of play.