Choose Geoffrey Longsword as your character when you start the game.

For the first moves, try to conquer the best territories till your army is almost wiped out (you get new men every land you take). After a few turns, you should have a considerable amount of money (if an enemy Lord steals your treasure just steal it back right away, this is why you must choose Geoffrey, his swordplay is great).

Spend it all on men and then go ask Robin Hood for help three times in a row (everytime Robin agrees to help you, you must choose a different territory than the one you were standing when told "Select a territory").

If you've done everything right, you should now have more than a hundred men in your army! Go and conquer all!