step 1: have a positive attitude towards the game in general. have fun every game and don't tilt. even in a loss, mute the toxic people and focus on yourself. always focus on your own mistakes to get better and try to correct them. eventually you will.
step 2: have a main champion that you play exclusively whenever you can that you are not only confident in, but know its your best shot to carry with. for all other roles, have at least one champion you can play pretty well and go even in lane with.
step 3: understand all roles quite well. if you say "god i hate support, i always suck at support". then practice support in normals till you are better at it. same with any other role. playing all the roles will help you better understand the game from all perspectives.
step 4: WARD. i mean this. as soon as you can. upgrade your trinket and ward areas that you need to ward for safety. baron/dragon are always imporant, but if you have to push up to farm then ward for yourself. the upgraded trinket is only 250 gold and is basically a sighstone. i always have 3 wards up as a solo laner even without sighstone. buy pink wards occasionally as well. you can use them to ward entrances to your jungle or ward key objectives like baron/dragon.
step 5: focus on learning the nuances of the game/objective control. remember, a game is won by objective pressure/lane pressure. not by kills. you can be 8/0, but if enemy team is constantly shoving down your team's throat and towers you will lose inevitably. you have to manage the waves, and apply lane and map pressure. sometimes that means making sacrifice elsewhere, but once you learn when a trade is good to make you will always do it.
step 6: if you get an advantage, use that advantage to help your team. this does not mean going bot, getting yourself a double kill then immediately recalling. if you kill your lane opponent or force htem out of lane, just hard push in, take your own tower. once you get your own tower. kill them again, or hard push in and force enemy laner to stay in lane to take their cs. then you roam to another lane, force them out/kill them and take that tower. once all 3 lanes have their towers taken, you can group and push a lane or fight over an objective like dragon as your team is inevitably going to be stronger. this doesn't always work, but in my experience, snowballing your advantage is pretty key to carrying. if you cant help the other lanes or screw up your ganks, it could be the difference between a 20 minute surrender, and a 50 minute nailbiter.
those are the very basics.