For most adventures are guides available (check the list on the left).
For multiplayer adventures it can be interesting to take a lootspot:
- Example: "Complete "Sons of the Veldt" without using crossbowman, elite soldiers or cannoneers"
- It's doable but expensive on other units & for achieving it only counts your part of the input on the adventure. Taking a lootspot will take only cavalry or recruits. It doesn't matter how many rossbowman, elite soldiers or cannoneers the other player used.
- The other way round hand you can play using crossbowman, elite soldiers and/or cannoneers as much as you like and still sell them for the achievements.
So it's worth finding a friend and swap the lootspots to get both that achievement on a fairly easy way.