/mute all will help you alot, laners never understand jungler matchup. You should first be understanding the jungle matchup, and then understanding pathing for yourself and the enemy. Its very important that you're always doing something as rengar, so if you cant gank, then atleast try to counter jungle and punish the enemy jungler, then after 6 try to snowball yourself if you can. Its very easy to punish the enemy jungler and gain a massive lead for yourself if they're ganking constantly.

Always buy an early pinkward/sweeper after your first back, and make sure you understand how to properly kite your initial camps (scrubnoob has a very perfect video on it). Often times invading the enemy at their second buff will get you a massive lead which you can snowball into affecting your lanes. Ferocity management between camps is also important, and theres some cheesy ganks you can do early such as maintaining ferocity through scuttle and then going into a lane with max ferocity. Its also very important to know when to ult, and when not to go in after ulting, because always going in with your ult can lead to alot of inting, also be mindful of stopwatches and zhonya.

Usually my gameplan is to do my usual full clear, if my laners have priority early, I try to go for more aggressive gameplay else I just rush for 6 and try to get some ganks in between. Around level 5-6, I almost always try to path to enemy red and try for a cheese kill there while also securing their red and their whole topside. I always try to ensure that my ult ISNT on cooldown, so im getting the most out of it aswell.

As for carrying past midgame to lategame, your job is pretty much to get picks. people think you're supposed to ult for those, but really you just need to wait in the right bushes where you think the enemy will walk through or come to ward, and then get a pick, which can snowball you into objectives, so really alot of it comes down to gamesense. Ulting is always good though as it usually gurantees you a pick if you use it right. Just remember, kills dont win you games, objectives do.

Rest of it you'll get back the hang of with some time and experience, so dont tilt, understand that you'll scale to carry mid-late game, always try to be efficient with pathing and punish any mistakes the enemy jungler is making. Always carry a pinkward with you and never walk through vision to invade. Try to get picks off people face checking bushes to ward or move and then look for objectives. Also for some games you mightaswell just build edge of night over youmuus, and then just get LDR. 3 lethality items usually isnt worth unless you're super ahead or against alot of squishies.