Somewhat-experienced player, but still need some advice!

ALRIGHTY THEN. Bullet by bullet...

1. Ok

2. Runes and masteries are theoretically just a way to "customize" your character to your playstyle. Do you want to be more aggressive? USE DAMAGE RUNES! Do you want to be the team's frontline? USE DEFENSIVE RUNES! In reality though, they are just a way to boost the strengths of whatever character you are playing. Usually there are generally agreed upon "best" runes/masteries for a given character(s), with tiny differences (this time I'm going to use HEALTH runes instead of ARMOR runes because they don't do physical damage) based on matchup. They also give you a strict stat advantage over someone who doesn't have them.

3. Ok. Recommended items are pretty lackluster, they don't change based on your game (why would you be building a lot of armor if they do all magic damage), and are sometimes just not gold/slot/stat efficient. Learn what all of the items do and get an idea of why you'd build one over another (sometimes the difference is subtle, should I get frozen heart for the aoe attack speed slow? or will i be getting a lot, meaning that randuin's is better for the movement speed slow?)

4. This is a long point. At the non-competitive level, you have 2 people bot because it's closest to the dragon, and having an extra person there is going to give your team more control over this early objective. The two people are usually an adc and a support. The adc loves having another person there to make sure that they don't die all the time and can instead focus on getting money from minions, and the support helps them do that through buffs/heals/tanking/cc. The mid lane is the safest lane due to it being the shortest, so sending unsafe characters makes sense. If say Ziggs gets caught out by a jungler, he will likely die, but if he has a defensive structure right next to him he'll be ok. Usually this is a character who does magic damage because you already have a dedicated physical damage per second dealer in the bottom lane, and by spreading out your damage types it makes it harder for the other team to itemize against you. You send one person top lane who can traditionally win lane/survive lane by themselves, and this lane we see the most diversity in what gets sent there. Right now it's a lot of tanks/utility at the competitive level (Maokai/Lulu/Mundo).

5. NA > EUW anyway. Welcome to 'murica.

6. Reckless isn't necessarily a bad thing, it just means that you need to REALLY know when to disengage. The ideal situation in a fight (if you're being really aggressive) is to get out with only 1hp. Know your/teammate's/enemy's damage so you can more accurately judge when you'll live/die.

I use Blitzcrank as my main (though I haven't played much of him lately, been trying new champions), with decent amounts of experience playing Lux, Gragas, Singed, Gangplank, Vladimir, Lee Sin, Heimerdinger, Cho'Gath, and Corki. I personally like playing Blitz (and anyone else) where I can get right into the fray and try my hand at killing enemy champs (which often gets me killed, but usually I do decent damage before I go out). Lately, I've tried Azir, Nasus, and Ziggs, but only Ziggs provided any fun thus far; I was a terrible Azir and a lackluster Nasus.

This seems like a decently sized champion pool. In my opinion, the best way to learn is to learn the fundamentals of competitive play on a few champions and then expand your champion pool.

I do not fully understand runes and masteries. I always have one point for the Improved Recall (since I recall a lot), and I have a few runes that mainly help Blitzcrank (or so my friend says), but I don't utilize either feature to their fullest, admittedly. They're kind of tough for me to understand...

Don't worry! They're one of the hardest parts of the game to fully understand. Until you hit 30/start playing ranked, I'd recommend just following a guide, as having specific runes/masteries for specific situations isn't something you really need to do even in competitive play. It's usually more important to focus on more fundamental aspects of the game rather than min/maxing your stats.

Usually, I don't stray too far from recommended builds once in-game. Occasionally I'll tinker with something different, but usually it's just a different trinket and nothing too different...

This is fine. With experience you'll be able to know the advantages and disadvantages of various items. Feel free to experiment. Nothing's stopping you.

I have trouble understanding which champion excels in which lanes. To me, top and bottom lanes are exactly the same with different sights to see, and so is mid, with the exception of it being slightly shorter. I originally heard that ranged-attack-using champions normally go bottom (and melee-using-ones go top), but then I see ones like Taric in the bottom lane and think "What?"

This calls for a somewhat longer answer:

The difference between mid and the two side lanes is that mid lane is shorter (And therefore safer as it's easier to get back to towers). The mid lane can also roam to either top or bottom during most points in the game. The two side lanes are different as bottom lane is closer to Dragon (which you will usually be getting early game), and top lane is closer to Baron (Which is not important in the early game).

Now, since you have 5 different champions on each team, it makes sense to have 1 person to each lane for all the experience and gold. It also makes sense to have 1 person in the jungle for the same reason. However, you're left over with one extra person. This person could go top lane, bot lane, or mid lane, as the jungler is already starved for gold/experience, or they could roam and gank, which leaves your team behind in the late game due to less gold/exp if they aren't successful.

The latter was the meta in North America for a while, but the European players found out that it was much better to have this player play as a "support" role, rather than roaming, and showed it by dominating NA in tournaments until they switched over. Champions in the support role have to share a lane with another champion, and it has been found that it is much better to have a champion who operates independent of gold playing this role, as this way, they can just split the experience and not get gold from minions in their lane.

This way, you can have a champion sharing their lane who is dependent on gold and not so much on experience. This person is nearly always of the "marksman" role, more commonly known as "adc" (Acronym for Attack Damage Carry), as their items are expensive and scale off of each other.

I have hit character limit (So annoying. the old forum didn't have this problem)

cont'd in next post.