3 Game Essentioals: Allies, Upgrading, Indestructibles
Some players may disagree with many of my more detailed views on how to optimize your wins / basse / income in MW, but I think many will agree with these basics:
These are key. At any level of the game a person with a high number of allies will be avoided by someone with significantly less allies. Remember that you bring YOUR units into battle - your 5 allies per level basically carry your 4 pieces of inventory equipment. High ally numbers do mean you will be attacked by mostly higher-ally players (and you will face certain casualties), but from what I've seen the attacker usually loses way more equipment than the defender (raids are almost never profitable, especially if you lose almost any unit). Keeping your allies high allows you to go slow and steady.
Again, you have to start off slowly if you want to build cash (cash is king in this game). Focus on leveling-up your air field, then buy Stealth Surveillance Drones. They are a bit pricey ($525,000), but they have a 30 defense - just one point less than the $1,750,000 Apache Helicopter - and have a very low casualty rate. Your defense stats will be epic.
2. UPGRADING (INCOME)
I came upon logical income growth by accident. I really didn't attack much at first and focused on building my protected income and base. I contend that you should ALWAYS BE UPGRADING THE RIGHT BUILDING, even at the expense of expanding your base or starting a new building. I also recommend upgrading the highest income producing building that pays out over a LONG term and NOT looking at cost / benefit.
Example: Face it, Supply Depos (and Armories and Storage Silos, etc) suck because they require you to play constantly to fully optimize their income potential. Upgrading takes a LONG TIME, and the time you spend upgrading quick-producing buildings, while more economical from a total cash flow point of view (I.e. you hypothetically make your money back on upgrading a Supply Depo in 1/3 the time as an Oil Refinery), you will never fully collect all of your investment. Not by a long shot. Early in the game focus on upgrading your Command Center, Wind Farm, Market, Stockpile, etc.: You will almost always collect on a 12 or 24 hour building, but you'll probably only collect on your Armory 1/6 of the time. Always be upgrading and attempt to upgrade your highest-collectable building. By LEVEL 90 I was making about $350,000 per hour, and was probably collecting $300,000 of that (and no, I haven't spent money on any buildings). If given the choice to build a new building or upgrading at a similar cost you should upgrade.
High income means you can completely avoid raiding (which is way too costly for my tastes).
A side note on high-end upgrading: You can't protect more than $10,000,000 (you should upgrade your protected amount as quickly as you can). When you start getting high up for upgrading it is hard to avoid losing funds to attacks. The best way to avoid this is by using 24 and 48 hour buildings. Get up to $10,000,000, then wait for all of these synced buildings to generate. If you time this with your 12 hour buildings you can get a nice boost (I can sinc almost $7,000,000) and do a mega-upgrade (like a Level 4 Oil Rig and Chemical Plant or Level 6 Oil Refinery).
3. INDESTRUCTIBLE UNITS
If you ever want to battle you will need as many of these as you can get. Battling is brutal on your high-end items. If you have a money generating base you can open every box in a "box" contest, fight epic baddies, and win up to 3 indestructible units for each. I have yet to win 4 in any contest, so I'm guessing it is nearly impossible unless you spend real cash.
Lastly, just to reiterate, you should start the game off slow. Don't battle too much. This way you fully capitalize on Valor missions once you are a strong fighter. I just bacame Lieutenant rank and have 40,000 valor points. I don't battle beyond mission requirements except for revenge, so I am hoping to have about 80,000 by the time I rach Major (then the real purchasing begins). If you have enough income you can afford to trade cash-unit casualties for those awesome units at the height of the game.