Hello. I have a few advices for you in how try to help him:

• first in which position he plays (adc, jg, sup, etc);
• even though he queue up for another match, tell him what he did wrong or ( if he is playing at the moment) try to connect with at discord at tell him in real time what he should be doing and why.
• how much does he ward in a match. That is some real problem, because most of the people in game doesn't know the power of a ward and doesn't know to place them. If, you're not a support, you have less control of wards, and as I said people doesn't know how to place them correctly. So, especially if he's playing low elo (platina and down) he should place wards for him, in a way, he can know what's happening in the game and avoid gank.
• items to buy, how to counter the enemy team as much as possible. Most people only goes with one type of build, always with tabi (if you're top) or always with berserk boots (if you're adc) and they SHOULD NOT do that, of course most of the time they will you use that, but if you're in disadvantage buy items that can help survive in the game even the boot ( like a swiftness boot for cc or mercurial boot for heavy AP ) and of course always tell him to check the enemies build
• what does he do at the mid game? That's a problem that even high elos have, most of the lol players doesn't know what to do during the mid game. And that's only gran masters and higher have more awareness of what to do during this time of the game. Because if you're winning or losing during the mid game you still have 4 places you can push and farm ( the jg, and the others 3 lanes). Most of the time happens of 3 people being in a single lane during this time. Why? They're not even farming correctly. During the mid game is when you can get an advantage in items. If you're not being able to push anything ( and That's hard to happen) go walking around the map and put some wards. Buy pink, place normal wards throughout the map so you can see what the enemies team is doing.
• but in the end which lane, as said before, is the most important one. If you're playing in lol elo, then you should not go as support or adc (in ranked) first because as an adc is terrible and almost impossible for him to carry a game because the top and mid enemies always will be more stronger.