[1] Your role preferences seems to be all over the place. I would highly recommend narrowing your selection down to two roles. This will let you get a better handle on the general mechanics of that role at all stages of a game.
[2] You seem to be choosing a large variety of champions rather than sticking to a smaller pool. Until you improve, I would recommend you focus on ~3 champions per role (for a total of 6). This will let you focus on learning more about that champion's play-style, build paths and role at various points in the game and as the situaiton varies.
[3] I would recommend you play mechanically simple champions. You seem to be largely doing this already, but it bears repeating. It will let you focus more on learning the fundamentals of the game instead of having to worry about playing your champions optimally.
[4] Prioritize farm. Farming is the most reliable source of gold and experience in the game and it can make you far stronger than you appear to be. This is true on every champion and especially early-game; a difference of 100G can result in you returning to lane with Phage instead of a Ruby Crystal, Long Sword and Boots of Speed.
This is especially important when you realize that ~15 farm is equal to a kill. Take the free gold from minions; killing your lane opponent is often secondary (and much easier when you have an item advantage from better late-hitting.
Just remember that gold you haven't spent does nothing for you. If you are a couple kills ahead of your opponent but are sitting on 2k Gold while they have just bought, they are probably stronger than you are.
[5] When necessary, build defensively. If you want an example, I'd honestly rather a 0/2 Darius with Phage and Sunfire Cape than a 0/5 Darius with Black Cleaver. The early durability helps you survive the laning phase even when you are losing; you can finish your core damage items after when gold is more plentiful and you are less likely to be bullied off of farm.
[6] Learn to control the minion wave. This is especially important in top-lane, where a proper freeze can result in the enemy laner missing several minion waves worth of gold and experience very easily. If you get a lead, use it to deny your opponent; it lets your free-farm and puts them further and further behind.
[7] Learn to farm efficiently. This is especially important when jungling, since you have to keep up in gold and experience while having access to less farm than laners, controlling objectives and (counter-)ganking. If you are playing a jungler who relies on being ahead of their enemies, learn when and how you can take lane-farm without denying your allies.
Several examples of good opportunities to soak farm are:
- holding the minion wave when your ally is recalled, dead or roaming
- pushing the wave under the enemy tower after getting a successful kill (then proxying the next wave if safe to do so)
- split-pushing or wave-clearing during the mid- and late-game.
[8] Know when you can trade with your opponent. While this is often up to experience, you have to watch for when your opponent wastes a cooldown (either because they used it to farm, missed it, just used it to trade, or you baited it out) and take advantage of its CD window.
Know when you have an advantage in (live) minion. Those little guys really hurt early-game.
Know roughly when champions hit major power-spikes and try to take advantage of yours while avoiding theirs.
You might be able to get more specific advice if you tell us what your main roles and champions are or if you have any specific questions.
