Hello all, thought I'd drop in and share some of my secrets...if you can call them that.
Okay, first of all, let me introduce myself; I'm at level 106, legitimately mind you, with only Stalker, Operator, and Infiltrator to complete, and I am about 20% done with commendations.
A nice easy way to level is going to the store, and getting codes off of doritos bags for Halo XP, I wish I'da known about it before all that Mountain Dew I bought >.<. Mind that you max out at 200 games. Sell the excess to buy pre-order armors or specializations off ebay (how I got Dead-Eye and Locus helmets)
That being said, it takes about 300,000 XP or so to get through a specialization, using Fast Track from Pioneer coupled with Double XP points, playing Spartan Ops (currently the most profitable is The Didact's Gift, and the quickest for those without Double XPs or Fast Track is Rally Point on Episode 4) with the most profitable giving 13026 XP a game will take 23 Matches. Also mind that when you end a specialization, any overlap XP is lost, so play spartan Ops alone when close to completing, as it won't waste your XP points. ALSO be mindful that there is a cap, you'll reach roughly from Level 1 to 7 or 8 before you hit the cap which is about 200,000XP. The last two levels (8 and 9) are 60,000XP each.
Keep in mind also which enemies you need to kill and focus on where they spawn in the match, the only ones I need are Jackals, Grunts..and Zealots for Covies...and all but Crawler Primes for Forerunners. You get a lot of XP from completing those commendations, but they do not double with Dew Points. Neither do Daily Challenges.
Make sure you do the Campaign challenges, they're really easy and they do't waste your Dew XPs.
And lastly, the lightrifle is THE best gun in the game. Why? Because it takes 3 hits to make a kill. Two scoped to the head, then a melee should kill an opponent. 2 shots faster than the DMR and 4 faster than the BR.