Find people you like to play the game with. While I think the community's toxicity has been largely exaggerated, as most of the playerbase is just fine, it can still get quite bad at times and playing with friends makes things much better. Also, don't get drawn into the stupidity when someone does get toxic. Just mute and ignore them and you'll have a much better time at the game.

It's best to spend some time early on playing against bots so you get the hang of the game's mechanics and find out what different champions do.

You need to Master Last hitting... for CS.

So the idea is you dont "miss" any income by not getting the kill shot on the minions.

Play vs bots and practis until you get good at this (dont just auto attack constantly).

Take like 10-15 matches vs bots, and just focus in not missing 1 cs.

Then start playing "normal" matches.

Here you can try to harras the lane opponent playing against you, so he/she misses CS (and you ll experiance them doing the same to you).

Thats the micro elements of the game (who can CS better, while harrasing the other).

Whoever picks the better champion into another, and plays their champion better, is going to have more money in their lane.

The macro stuff.... the "think big" stuff.... dont even worry about any of that yet.

If this is your first day just keep practising CSing.

You need to pick 2 roles to practis though (because you wont always get your main role).

Between Jungle, Support, ADC, Mid, Top.

Do you have a social life? If you do start making preparations to say goodbye to it.

1. Try to stay alive longer by reacting rationally.
2. Check the mini-map often and try to improve your awareness, knowing where are your allies and enemies at all time.
3. Try all roles and champions when you get the chance, so you've got a better idea on your opponents' capabilities and it's easier to find patterns then.

^ Or this

Depends on who you're playing with. The highly competitive based players can be toxic, however those that play against AI like I do on Heroes of the Storm, not so much. I find playing with other human players vs brutal AI to be less stressful and less toxic than playing ranked vs other human players.

@OP

If you find it a bit too much for your liking (even after taking some practice matches vs bots for example), you could always give Heroes of the Storm a try. That game doesn't deal with gear, but instead with talent choices.

Don't chase people into their tower for a kill. You will wind up dying to them.

Don't chase people into the jungle past the first three meters. You'll get ganked by their team.

Always buy a ward after your first back. Put it in the grass next to your lane.

Never push enemy minions all the way back to their tower. Once you get that close the enemy jungler can gank you, before you have time to make it back to the safety of your tower.

Try to outlast your opponent and make them recall for health/mana first.

Nasus, farm, q stack.
Enjoy.

Malzahar. Hit E and walk away, for free farming. Need to kill an enemy champ? Mouse over them and hit Q,W,E,R. Been wrecking people like this for years. 

I assume you're talking about my suggestion of him trying Heroes of the Storm if LoL isn't his cup of tea?. It's not the "wost" moba out there, it's actually quite fun and competitive to boot as well as sporting heroes from various Blizzard games, making it easier to identify each character.