You'll usually lose raids early on, especially if you're a peace clan, because your clan magic is small and you don't have enough warriors. Some tips for winning battles successfully:
- In the beginning of the game, don't raid more than once every 3 years, especially if you're a peace clan. You shouldn't really raid the first three years at all, but focus on building up your weaponthanes and defences.
- Put most of your weaponthanes into patroling the outer ring, not the inner one, because that's where they'll spot raiders. Make sure to check your patrols every fire season, because explorers and traders will take weaponthanes away from patrols and they aren't automatically put back when they return.
- Have a good supply of hunters (30+) because they also spot raiders and they're useful in battle.
- Raid as little as possible. IMO, you should only raid when your battle magic starts to become ineffective.
- Make allies with everyone surrounding your tula. They'll sometimes warn you when someone is invading. They're also the ones most likely to raid you and it'll dramatically reduce the likelihood of that. End any feuds as soon as possible.
- The handiest battle sacrifices are the Humakt ones, so concentrate on those early on, especially Truesword. When you can afford it get the sacrifices that reduce deaths among your weaponthanes and farmers, because then even if you lose raids it's not too big of a deal.
- The best sacrifices for protecting your tula are Fyrdwomen and Watchfulness.
- Always sacrifice to Humakt before a battle unless you're going to evade. His sacrifices seem to be more effective than sacrifices to Orlanth. If evade is your battle strategy, sacrifice to Orlanth or don't sacrifice at all.
- The Humakt heroquest really helps with winning battles early on, and has some good treasures that can turn the tide of battle.
- The ideal amount of magic to put towards a battle is about 5, but you won't have this much until late in the game. Put as much as you reasonably can towards it (1-3 points), because magic does have an effect on the outcome of the battle.
- If you're the one doing the raiding, go during storm season, not during fire season. Other clans expect raids during fire season, but you can often surprise them during storm season.
- Adapt your strategy to how many people you're facing. Charge is the worst strategy in my opinion, maneuver is the best. Maneuver will work most of the time. But if you're massively outnumbered, use skirmish. If you're trying to do a cattle raid and get spotted, use survival & evade unless you have more troops than they do.
Even with all the sacrifices and treasures and lots of weaponthanes and footmen, you will still lose battles about 1/2-1/3 of the time. That's just the way of the game. Rebuild your herds through trading, favours and questing, and the occasional cattle raid.