Not a supreme master like a lot of those folks in chat, but some of the things that help me out the most...
Major basic things:
If you're attacking a neutral (2) with 3 troops, do it as your last move. If an enemy hits it first, you'll take it from them. If you're attacking with 4+ plus troops do it first turn, so that when they attack with 3, they'll bounce off. Dont attack unnecessary neutral territories (generally only take territories that clear you up to take a bonus or position you toward an enemy. Rarely need to take extra parts of a bonus prior to taking the whole thing, although income may force this). Check "Analyze Attack" often, and make SURE you know if you're playing a luck game or not--if 0% luck, avoid attacking neutrals with less than 3(there are times to pull a 1-2 v 2, but it leaves you in a worse position than a 3 v 2.)
Troops on defense are stronger than troops attacking by default. A 10 v 10, both attacking, whoever attacks first loses(first defends, wins, counterattacks with stronger remaining). Avoid attacking in a losing situation. Two 5 stacks attacking someone is generally less useful than one 10, although 1 10 offers less defense. Can it sometimes work? yeah. Advised? No. That 10 stack hitting the 15 stack generally just wastes troops. If you know where an enemy is, work proactively to break a bonus by stepping in heavy the turn they're trying to take it. Conversely, while defense is stronger than offense, a bonus broken is better than a bonus owned, all other things being equal. The time and troops it took to claim a bonus are all wasted so long as the bonus is broken, and they must use their early turn moves to clear you out of their bonus. So play offensive, particularly if you are at a weaker position than your enemy--this does NOT mean attack a heavy stack with something weak, it means try to screw up(by breaking them or threatening them) as many bonuses as you can. If you get kept on the defensive against someone stronger, you will get weaker each turn and will die. If you break them up, they'll have to worry about reclaiming their own by attacking your troops moving through their bonuses and will divide their income.
Watch history of the turn before to see how your enemy moves and what their income is. Those spare 1 troops laying around? Shuffle step with them to delay turn orders--it is almost never preferable to attack heavy in the middle of the turn. You can use those troops to essentially force your enemy to move first and then react to them. There are reasons to attack early(to slip in through an enemy's defense and break their bonus or to catch an enemy whose screwing with you, or to move troops into or out of a defensive position unexpectedly) and late(to fend off the enemy and counter attack, to retake a territory they took early), but rarely in the middle. In games with a stated turn order PAY ATTENTION TO IT.
In team games, communicate. Read chat, check your teammates orders if you like, whatever, but playing as a team beats going it solo far more often than not. Even if you're screwed, keep fighting. You can often wreak absolute havoc even with only 5 income by breaking bonuses or slowing down an enemy and help your team out a load. The MVPs of your team often have low income at the end--they've instead enabled the others to grow and dominate the map. Try not to piss people off, even when it's tempting. Try to never get booted. Dont play too many games at once that you cannot keep track of them/play them ably.