Many players don't understand the importance of a good team composition at even a basic level such as the need for a jungler, this of course isn't a problem in higher ELO ranked games, but in the beginning stages where you get someone going "get in lane" etc, is quite poor and when no one feels the need for a tank, or a support, or all go melee DPS or AP nuker, these teams do not work and a team needs to be balanced within reason, I feel there should be an article for this as it could really help people just trying to start ranked with what they need to be trying to acheive, per say at least one champion for each role ie. Ranged DPS, Mage DPS, AP Nuker, Melee DPS, Support, Tank, Jungler, Offtanks, Carry, Assassin etc.
Obviously people can fulfill two of these rolls, Carry, Tank and Jungler being a different set of needs, however Rammus, Nunu, Amumu for example can all function as the tank and jungler for the team. Tryndamere and Yi can be the carry and jungler.
If just two people on a team could do this (which is viable in a solo queue to ensure) you can make a good team comp, obviously not the best, the best team comps are for premades, which you slowly fabricate and make happen, and because of Draft Mode, you want several comps which you can adjust into with some degree.
I should note that a 2 v 1 lane player is a good thing for a player to be able to do at low ELO where teams may not run a jungler, as certain champions (Heimerdinger who can even push in 2 v 1) are more equipped to deal with such a scenario.
So yeah, Team composition and Team play, the roles of various classes and things teams should include.