EDIT 2013-10-29
I wrote this guide a few days after Modern War’s late November 2011 release. As such, it is likely significantly out of date when factoring hindsight and game changes over a two year span. Please verify information herein with contemporary forum posters. Please do not direct inquiries at me as I retired from the game as of February 2012 and am not privy to any activities since that time. See this post for comments.
Nation selection
UK (Sea Power) is probably the best end game option while China (Infantry) would be the best upfront. Germany (Ground Forces) and Russia (Air) would appear to be in the middle but are probably suboptimal options as sea units aren't significantly more expensive, if at all, and have the benefit of being more durable. I'd like to hear contrasting opinions. There's not much discussion on the topic, and I'm more of an authority on economics than PvP strategy.
Starter gold usage
You technically are not forced to expend gold during the tutorial. While the menu is locked, the timer is still active. Don't beat yourself up if you paid as there isn't anything one can do with the default 10 gold besides speeding up building (or buying a red maple tree). Gold usage for speeding up is max(int(minutes_remaining/12),1). Int() is the integer, or truncate, function, which means to chop off any decimal for a hard round down. For example, 24 minutes, 0 seconds will consume 2 gold (24/12 = 2) while 23 minutes, 59 seconds (23.983333 minutes) divided by 12 is 1.9986. Chop off the decimal and you'll end up at 1. Therefore, for maximum return on initial gold, use it to complete 10 buildings/upgrades with less than 24 minutes remaining. The earlier you use up the gold, the better, in terms of ROI. The max() function guarantees expenditure of at least one gold piece, even if there remains only one second of build time.
Money Building Spreadsheet
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Getting started
Build the Barracks as instructed then immediately upgrade it to level 2, which will take an hour. Meanwhile, build two of each money building starting from the least expensive and trigger a land expansion as you will rapidly run out of space. Next, you'll need to get 25 allies onto your list in order to get the $1,000 visitor bonus from each. There aren't (yet) organized resources like there are for Crime City. I suggest harvesting this forum then browsing the comments of the users who accept. App Store reviews are another source. You shouldn't have a problem with getting to 25 in less than an hour, two tops, if you just keep adding numbers while the total is under 25. Make sure to actually visit them to get the bonus. As you collect, take the opportunity to practice using the "Vault" option as it is not automatic. CoachPappy suggests dumping all 10 gold into the VIP system, which will free the player to manage his base and visit automatically added allies. Most likely you will still need to add a healthy amount manually, however.
Once the Barracks finishes upgrading, immediately upgrade one of the Supply Depots, which will cost $1,670. It finishes in 6 minutes. Now mentally set aside $1,670 to upgrade the other Supply Depot and $2,790 to upgrade one to level 3, which takes 30 minutes. With the Supply Depot upgrade in motion and funds earmarked for the next ~40 minutes of upgrades, dump all your remaining cash into Engineers. Don't be shy. The 5-7 you'll be able to afford right now will adequately protect you from level 2 attackers, but they come fast in this game.
Soon you'll be rolling in cash. Your income per hour will exceed $13,000 after a little more than two hours invested. You'll get a significant amount of supplemental income by defending against attacks from players who forgot to vault their money. Next upgrades are the other Supply Depot to level 3, Armories to level 3, Storage Silos to level 3, Supply Depots to level 4. Keep packing on the Engineers. You'll want a minimum of 2x defense to your top rival's attack. Then up that to 3x to give the middle finger to the constant wave of attackers. Don't worry about the high casualty ranking. With so many Engineers you'll totally overrun the opposition and keep them all. 15 Engineers is a good starter amount for levels 2-4, but with the constant wave of attacks you may level up when not paying attention so it helps to be prepared. After 15 Engineers it is recommended to switch to Transports. Modern War allows five allies per level and four units per ally. Worked out, that means up to 20 units at level 1, 40 at level 2, 60 at level 3 and so on.
Once you've set up base camp, so to speak, it's up to you. You have a lot of breathing room as long as you avoid PvP, questing, and goal accomplishment. Fortunately the War Factory isn't awfully useful in the early going, as it is a goal. The rest is wide open, though. I suggest proceeding in this order: always be upgrading money buildings, expand territory to fit all the available money buildings then construct them, add to the vault max, add more land to fit unit buildings then construct them. Remember to build new money buildings as your level is forced higher due to defending attacks. Stockpile powerful units until satisfied then move on.
Note that game mechanics have changed significantly since this guide was created so some items may no longer apply.
