For new players, I highly recommend checking out the League of Legends wikia page on Runes Here!

You can only have a certain number of Runes, and you'll want as many tier 3 runes as possible. Save up IP for them until Level 20.

Runes can actually make or break a league game. Flat runes boost your early game, scaling runes top off your late game. A League Summoner can only have 720 Runes, which seems like a lot, but all those runes would cost around 388,071 IP. Also, the strongest Tier 3 runes, total, come to a total of 684, so you can have 36 Tier 2 Runes without impeding yourself.

To make things easy, consider this... each type of rune scales well with a particular kind of stat. If you prefer, you can get actual percentages Here, on the Wikia page for exactly what rune is most effective where. You will get the best performance in game from Runes that are highly efficient in their respective categories. As an example, you'll get better performance from a page with a few of each stat and specialization in one, rather than only one stat. As a rule of thumb, consider the following.

Shh!

Seals are best used for defense (Armor/Health). Cost between 102-820 IP each, and between 918-7380 IP for a full set of 9.

Glyphs are best used for ability offense (Ability Power), ability defense (Magic Resist), or Utility (Cool Down Reduction/Mana Regeneration). Cost between 102-820 IP each, and between 918-7380 IP for a full set of 9.

Shh!

Marks are best used for offense (Attack Damage, Attack Speed, Magic Penetration, Lethality, Precision) Cost between 102-820 IP each, and between 918-7380 IP for a full set of 9.

But Quintessences...

Can be used for all these and more, but cost from 512 IP each to 2050 IP each, or 1536 to 7150 for a full set of 3.

The reason for this guide is to give new players an understanding of the importance of the Runes. The idea is to save up enough IP so that when you hit level 30 (and eventually ranked play) you won't have wasted very much IP on runes that aren't optimal for PvP.

These are the most popular Runes in all of League of Legends, courteously taken from League of Graphs.

For one basic flat Rune page without quintessences. 2754 IP

Runes are very expensive, so before you go buying every champion in the league, you'll do very well to yourself to save up for runes that can be swapped between champions. Most ADC's use the same rune page, but most other champions get fine tunings that allow them to perform better in certain ways during the early game.

While not the easiest tool to use The Runepage Calculator does make it relatively easier than using the Client Store on League of Legends, tells you how much the page would cost. Also, rather than buy pages for full price, every 6 months in May-June and November-December be on the lookout for Runepage sales where they two for 1 with IP or RP, and there is a discount on the bundle of 7 for RP.

What I consider to be the most cost effective Rune page would have to be for Attack Damage Carry's.

ADC's consist of most marksman in League of Legends. One Rune Page of:and this page applies to 15 Champions!

9/10 AD Carries are going to need:

x3

Greater Quintessence of Attack Speed (x3) Go to: 3 Third Tier Quintessences add up to an extra 13.5% increased attack speed, and is the single most cost efficient rune for these champions. At 3075 IP (1025 each), they seem very expensive, certainly. But they open you up to being able to play every marksman in League of legends as well as anybody else can!

Exceptions: Jhin / Varus : while these two snowflakes can do well with Greater Quintessence of Attack Speed, it's more common for them to take Greater Quintessence of Attack Damage.

x9

Greater Mark of Attack Damage (x9) will make last hitting minions with auto attacks (A.K.A. Farming/ Creep Scoring) much easier, and is taken on EVERY Marksman. At 918 IP (102 each), these are pretty cheap, and actually end up on tons of other rune pages.

x9

Greater Seal of Armor (x9) will allow you to have a bit of proper resistance for trades in lane. These are the most common defensive rune stat in League of Legends, and neglecting these only leave you at a disadvantage. At 918 IP (102 each), these are the cheapest tier 3 Seals, and actually end up on tons of other rune pages.

x9

Greater Glyph of Magic Resist (x9) will allow you to have a bit of proper resistance for poke by the enemy support in lane. Occasionally you'll see these swapped out by extra Attack Speed, but Magic Resist is more efficient.