1. Strike first, and strike last. - A small strike before your opponent can stop it is better than a large one once he can. Practice being fast through the ages, it's one of the few things you can practice against the computer since military is irrelevant.
2. Having a large economy is extremely important. I used to completely ignore micromanaging my armies, focusing all my attention on economy, occasionally taking a moment to send more troops to the battlefield, and winning. Meanwhile we constantly see new players training large armies while having tiny economies of a dozen or so villagers, and being unable to sustain more than one wave of combat.
3. Keep growing your economy! One of the reason I'm not as good as I used to be is people now play with 200 pop, whereas when I used to play it was almost always 50 pop. Because of that, I often forget to grow my economy past the first 40 or so villies/boats. Don't make the same mistake, grow to 150!
4a. Good units for offense: axemen, scouts, bowmen, warboats, cavalry, CAs. Slingers and STs are good support to take out any walls, towers and buildings the enemy may have, and do well against defensive archers also.
4b. Good units for defense: walls, bowmen, slingers, camels, compies.
5. Civ is indeed important. Some civs are fast, some are strong, some are unusual and surprising... and some just suck. Don't use random, greek, cho or carth in RM unless you're looking for a challenge.
5a. Shang is one of the best civs for new RM players because the reduced villager cost always helps no matter what your strategy, and their wide variety of units lets you try most strategies you hear about. Also be sure to build walls, they can often give you more time to prepare if someone is about to rush you, and that can make the difference. 5b. Yammy's bonuses, as I mentioned in another thread, are very well focused for surviving and counter-attacking against tool rushes of all kinds. As they become less powerful in later ages, you have to learn how to be faster and more offensive - but they can help you avoid getting crushed early on.
5c. Mace has very powerful bonuses for bronze land attacks, but what is more significant if you're just starting out at zone play is their villager see much further. That means you can find berries, forests, gold mines, and lions much easier.
5d. Rome has cheaper buildings, which like shang's cheap villagers applies no matter what you do, and is even more significant on land maps once you start farming. Their tower bonus can be nice in tool age and their cheap buildings can help them mount a mixed tool offensive more easily, but their bronze age is weak due to a conspicuous lack of archery units.
5e. Minoa has much cheaper boats, by far their best bonus, which allows them to both win the sea with large fleets of warships and fully exploit it with masses of fishing boats. Minoa's second bonus would be composite bowmen with extended range, which can be a powerful military bonus as composite bowmen defeat chariot archers in large battles; however, as compies aren't as fast as CAs, it's harder to use them offensively so you may have to rely on camels for that.
5d. A fleet of hittite's long-ranged warboats can defeat any other until late iron once you have enough of them. Their archery bonus applies well to archery units from tool to iron, giving them a small but useful military bonus throughout the ages. Their siege bonus makes them one the the major powers in iron and evel late bronze, if they aren't demolished early. In addition to all that, they have a wide variety of useful units so they have the option to surprise their opponents whereas every good player knows what to expect from civs such as yammy or minoan.