Okay, ze list !

1 - Get familiar with ALL champions. That means trying out
champs you haven't tried, each week when they're free, at least
1-2 times. Both so you can sense their timings, use of abilities
and how much their abilities might scale with AD and AP for example.

2 - Watch streams and other videos. Many times, there will be direct
links to streams of some popular streamers, in the LoL client. If not,
sites like youtube and own3D.tv are good sources. There you can watch
how people make good, as well as bad plays and see if you can take
something away from it. For example, one mistake many beginners make,
is that once they get saved by an ally and survive with low health, walk
back to the enemy for one reason or another and end up dying for it.
You may notice that you do this, when you see someone not do it in a
video.

3 - Keep up to date on patches, by viewing the patch notes. Again, these
notes are linked to in the client, when they're out. They're important because
they can mean that an important ability on your favourits champion, now has
a longer CD (Cool Down). Or that someones damage has been nerfed, thus you
can afford to play more aggressively against them perhaps or what have you.

4 - Joining Mobafire in houses is also a way to get better. You can receive
critism from fellow players on your performance, depending on which inhouse you
join. This is useful because you can't always see your own mistakes.

5 - Heading over the Mentoring forum and making a new topic, can land you a mentor.
This is useful, because you might have a lot of unanswered questions. Plus, you'll
get someone who might be quite a skilled player too, meaning there's room for you to
learn from them.

6 - Creating custom games for yourself, where you practice basic things such as
last hitting minions, warding and/or communicating can be great too. Last hitting
is especially important and can be done alone too. In higher level play, getting
proper farm is important, since you can't count on getting early or many kills.
When it comes to last hitting, as you get better, set goals for yourself. For example,
try to get 200 last hits by 20 min. First in a custom, perhaps versus a friend
or bot and then in a real game.

7 - Following a guide or three, can equally also be a good way of learning.
Even if you think you know a champion well, reading up on a guide about that champion,
can still yield some tips and/or advice. Plus you'll be exposed to different reasoning,
as to why you build a champion one way or another. For example, many beginners like to
build mages like glass canons (very strong, yet very squishy too) and that is one way
of doing it. Yet, in many guides, a balance is often tried to be found, meaning that
one or more defensive items will also be included in the build.

8 - Follow one of the (many) threads on Mobafire or elsewhere, of people on their journey
to a specific ELO. In these threads, games are often broken down by the OP (Opening Poster)
and as such lets you get insight into the thoughts of players more experienced than you
potentially. It also lets you see some builds of other champs, perhaps at high ELO play,
via screenshots.

9 - If you go unto the official league of legends website, you can find tips and tricks
ranging from beginner to advanced. In this forum, concepts will be mentioned, concepts
like zoning. Get to know all of these concepts and learn to apply them in your games.

10 - Experiment with the champs you have. Try different masteries than is the norm, try
different runes too and item builds. Maybe you'll find interesting builds and/or combos
you can use to your advantage. Plus, even if you don't, it can not only be very fun, but
you might find an alternative way to play, that can surprise your opponents.

11 - Get together with friends and think up interesting lane combinations. Even if the
combination is a very much known one, such as Vayne + Blitzcrank, it's still good to learn
how to work together with a teammate, as it IS a team game. Also, knowing how different champions
abilities synchronize, can help you create interesting and good team compositions.

12 - Be positive and communicate with your team; even in the pre-game lobby. If you play draft
mode for example and you end up as Captain, don't be silent and just ban who you wish
all the time. It might carry over to ranked games and that just plain sucks. Because maybe you
wanted that Darius banned, but instead someone else gets banned. Or maybe you didn't want
that Vayne banned, but she got banned. This can be detrimental to your team. However, if
someone is just impossible to reason with and it's really neccesary, instead of flaming,
hold down TAB and click the blue speech icon outside the offenders name, in order to mute them
and end things there. At least it'll help one of you focus on the game.

13 - Ward your lane. Many people think it's only up to the support, but when you recall, if
you have that spare 75 gold, it doesn't hurt an awful lot to pick up a ward too, to help keep
your collective map awareness up. In addition to this, learn some of the best ward placements
and get into the habit of robbing your enemy of their own wards, through the use of oracles
or vision wards. If you have a jungler, remember to tell them your lane has been warded, if you
saw it. If you don't, don't rage when the gank fails.

14 - Towers matter. I see this all too often, that my team doesn't push enough towers, despite
sometimes even being in the lead, in terms of kills. Towers win games. You can have 99 kills
and still lose if you lose all your towers and thus eventually your Nexus. Of course, it IS
more challenging if you're fed or if your opponents are, to take towers. But there's different
tactics for taking down towers and you should get familiar with them. Such as the split push,
wherein some teammates go mid for instance, while you push top with an ally. Downed towers provide
your team with gold too, which is not unimportant.

15 - Secure buffs and objectives and help your team. Killing dragon whenever its up can really
boost your team and sharing that red buff with your AD carry, instead of taking it yourself, can
likewise also make a big difference. Plus, it can also help raise morale, which means people
wont say "surrender 20".

16 - If you go to custom games and click "join" a lot of games will show up. Well, in the
top right corner, there's a great search bar. If you input "mid" or "ARAM" you'll find some
fun game modes on the map called Proving Grounds. This gamemode typically features a random
champion selection, meaning you'll get a random champion. That alone, can force you into playing
champs you have, which you might not be so good at, or initially like. ARAM stands for All
Random All Mid by the way and is a great gamemode.

17 - Using software like Fraps and lolrecorder, you can record your own games, for later scrutiny.
That can be invaluable to your game, for many reasons. Like some, you can then share it on sites
like this, to get other peoples opinions.

18 - Generally, try set goals for yourself. If you die a lot, try set a goal of dying less.
Many high ELO players die very very few times in each match, which is one way of contributing to
you winning.

19 - Don't go too long without playing. Many of the best players play all the time. Some people
are even full time gamers, so they naturally get a lot of practice in. Even if you don't think
normal games do much for you, they can, if you think more carefully about how you did in game
and can play successive games to see if you can do different/better.

20 - Join a clan/guild. These organisations can often help you get better, by virtue of having
members you can befriend and play with, as well as learn from and talk to. Playing a 5 man
premade, using VoIP is also worlds away from just playing solo Q by yourself.

Good luck ;)