Top advices - League of Legends

Well, actually you can learn farming better with practice, there is no magic. 

Learning lane control is important, you can win harder matchups just with proper lane control. (especially in lower tiers)

I can't really tell you how much agressive should you be, there is too much factor to give you clear answer. Actually if you are clearly stronger, sometimes freezing the lane and zone the enemy is enough... at least less risky than attack your enemy with sacraficing your escape. (without ward) If you think you are stronger, but you are not sure you can kill the enemy without sacraficeing yourself just don't do that, there is some case when it's worth, but the most important thing you should learn is playing as safe as possible, your team profit from it more than a kill.

If your laning opponent is leave most time you shouldn't follow him, because in that case he will know what you do and as you said, they can kill you. But you should always punish him if he leave the lane, you can choose between push the wave to tower and proxying a wave, push the tower, freeze the lane, farm jungle, if you need go back to shop and get item advantage while he roam etc.

If you pushed your enemy tower you should push your lane and invade the enemy jungle (with wards ofc), gank mid, force a dragon etc. But try to save your tower if you can, so don't stay too much far from your lane.

If you lost your tower (and your lane) it's a bit harder, you can freeze, but then your enemy will roam, it depends on the situation actually, if your team want to group somewhere just leave your lane, 2nd tower is relatively safe in that early phase of the game.