Cool, thanks.
I dunno. As I said, I'm not very good with military.
This is the best article to get you started:
http://www.civfanatics.com/civ3/strategy/warmongering101.php
Sounds like you need to pick more fights. The more you war, the better you'll get. If I were to create a short list of things to help, it'd say:
1) You can never bring too many units to the party. NEVER attack with fewer than two units; ideally have more than 3 for small towns, closer to a dozen for larger cities. My personal rule of thumb is bring at least one attacker per pop in the city you are attacking, more on higher levels or when attacking tough defense (ie knights vs pikes, cavs vs. rifles)
2) NEVER attack with a damaged unit, unless you are attacking a 1 HP low-defense rated unit with a 4/5 elite strong-attacker (4-of-5 hp swordman vs 1hp spear, sure why not). Otherwise, you are simply tempting the RNG gods to screw you over.
3) NEVER leave single, damaged units unguarded, unless you are trying to draw enemy units in that direction (in which case make sure they can't actually get to the damaged units)
4) Use terrain in your favor. Lead your armies along hills and mountains, never attack a city across rivers unless you have overwhelming force (like a cavalry attacking a longbow). Don't be hasty; if it results in an extra turn before to get into position, fine. Better than losing a stack and becoming vulnerable to counterattack.
5) don't underestimate the power of artillery. A) you can destroy city improvements like barracks and walls that will impede your progress, and B) you can see exactly how many units are in a town, thus knowing how many units you should have to attack. Each time you damage a unit, it rotates to the back and a new, healthy one pops up. Once you rotate back to the first one you damaged, viola! You know how many are there. A stack of trebuchets is cheap and effective. Don't be afraid to put off an attack for several turns while the trebs go to work on the city.