Hey there, welcome to the boards!
theorgg gave you some good advice, you should take it to heart. Especially focusing the deck down to 2 colors. The disadvantages of doing this are that you lose some functionality R and G just don't have (like Breath of Life), but the big advantage is that you will be able to stabalize your colored mana base much quicker. Nothing is worse than sitting on 1+ specific colored card for multiple turns because you don't have the mana to cast it.
You shouldn't need to look at 3+ color decks until you
A) Get some good ways to filter out your basic lands (4 Rampant Growth, 4 Harrow, etc.)
B) You get access to many good lands that can produce 2+ colors without having to sacrifice to get that mana.
C) You have a particular combo deck in mind that requires 3 colors.
A focused 2 color deck can handle most problems (minus Red/Black which has a tough time with enchantments), so in essence there is no need to go 3 color this early in the game.
If you want to focus on Red and Green let me give you some commons (and some uncommons) that you should try to get.
Card Explanations can be found here
Red
Instant direct damage instead of sorcery damage. The reason this is important is because while red burn is extremely efficient, it many times cannot take out big creatures. Having instants in the deck allow you to
add damage to a big creature that you are blocking, effectively killing him. Good cards to try and get are...
Shock (common, 7th and will be in the upcoming new set Onslaught)
Incinerate (common, 5th and Mirage, will have to track these down some but they don't get better than this spell)
Flameburst (common, Odyssey, should be no problem to snag)
Green
Green does 2 things best. It Accelerates your mana, meaning it gives you access to more mana each turn than the typical rules of magic allow. And it gives you very efficient creatures, meaning you will get the most bang for your buck.
Mana fixers to get
Rampant Growth
Llanowar Elves
Diligent Farmhand (odyssey common)
Werebear (odyssey common)
Harrow (Invasion common)
Vine Trellis (Mercadian Masques common, will be in 8th ed in April)
Good creatures to get
Wild Mongrel (Odyssey common, a wrecking ball)
Druid Lyrist (odyssey common)
Yavimaya Barbarian (Planeshift common)
Gorilla Chieftain (7th common)
Spined Wurm (7th common)
Nantuko Disciple (odyssey common)
Lightning Elemental (7th common)
I recommend getting some of the new set when it comes out in October, it will have a lot of good cards (better than 7th) worth playing. I don't know how long you've been playing, but if you just started you might find it somewhat complicated, but you've get to get your feet wet sometime.
Hope this helps!
