In order to successfully attack enemy AI you need to get a scout report first in order to see what is inside the wolf lairs, castle etc. the more troops, wolves and defences there are in an AI opponent, the more scouts you will need to send to successfully get a scout report
Scouting Wolf Lairs
In order to successfully get a scout report from any wolf lair, send 2 scouts. You will never lose more than 1 scout trying to scout a wolf lair so sending 2 means you will always get a report.
Scouting Bandit Camps
My advice for any bandit camp is to send 4 scouts. Usually you will lose a scout or two on these depending on how much troops and defences are inside. Most bandit camps are very small but there are a couple which are actually stronger than rat castles.
Scouting AI Castles
The best thing to do with AI castles especially wolf castles is to send 8 scouts. Some castles can be heavily defended meaning you lose most of your scouts. There is 1 wolf castle that is so heavily defended that you will lose all your scouts and it is not possible to get a scout report unless you kill some of its troops first