Playing doesnt mean practicing. You need to understand your mistakes, and understand why you are dying. If you died, its your fault, period. Once you accept that, you will die less and less.

Secondly, learn strats, both macro and micro. Try to lead your team

Dont rage, be helpful, not hurtful to the team dynamic

learn a couple champions that can be played in multiple roles. I.e. I play Fizz and Hecarim mostly, I can take either of those two champs top, mid, or jungle and reliable win lane close to half the time, the other half i go even, and rarely do i lose. Having a few backups is nice also, I can play EZ and Jinx quite well in the ADC/ mid (for ez) roles. I personally dont support because its too hard to carry from that position.

That being said, if u pay support, play playmaking supports. I.e. thresh, blitz, zyra, annie, etc. or an amazing peel champ like Janna to save ur team. A good Zyra or Annie support can often times have most damage dealt to the other team with just a couple items. Zyra with Liandry's, sorc boots and void staff, just melts a team. Janna can be one of the most frustrating champs to face when you face a good one. Blitz and Thresh can setup picks for even the most dumb players to follow up on.

This is just the basics. I would suggest doing three things if you come back. First, record games, especially ones where you do badly so you can go back and watch them, to improve. Secondly, watch coaching videos on what to work on, like gravity's coach LS has a lot of stuff to really improve your game, which you can apply to the replays you're watching of your games. Finally, apply what you're learning IN GAME. Actively think about what you could be doing different if you're doing badly. Losing lane? Why? How could you be turning that around? What items do I have, what should I have instead?

Finally, ward! Learn where to ward more importantly, and when.