I stopped playing again on the last day of Season 1. I got extremely pissed off (the only time I've gotten so pissed off at a game) because, no matter how hard I tried, I could not get to 1249 rating (for the bronze banner). Granted, I was solo-queuing, but still... I think it's utterly ridiculous that one person can ruin the game for you. It's great that it's a team game, but only if you actually have a team. On that day, I decided I needed another break, since no game should ever infuriate me as much as I had been.

I had several people that I would group with, but they all slowly started disappearing, so I probably just burned myself out playing solo all the time.

To expand on Dark Dragon's comment though: flat Armour/Magic pen marks, Armour per level seals, HP per level seals, MP5 per level seals, Magic Resist per level glyphs, flat cooldown reduction glyphs and flat HP quints are probably the most important runes to get. There are a handful of others, related to the style of champion you prefer, but the ones I listed above you will use the majority of the time. My personal advice is to save all your IP for tier 3 runes, as some of them get pretty expensive. If you really want to buy runes though, just use tier 1 until you can get tier 3.