In early campaigns we just played series of scenarios - no special campaign rules. Then we had one elaborate campaign that had all sorts of special rules. The basic idea is that each warband decided which section of Mordheim (we had four or five) they would explore that campaign turn, and there were games if more than one warband showed up in the same section. As I recall, there were seven of us playing. Before you determined where you were going that turn, different events - and I think the scenarios - were determined for each area, so some areas were always potentially more profitable than others. We made some pretty elaborate lists of special events. Warband earned "fame" points, and the winner was going to be the warband that had the most fame points after a fixed number of games. We optimistically set it at 20 games. However, after about 8 games two players became sulky and dropped out (they were falling behind, and in large part because  they were whiney and annoying, and  they consistently angered all the other warbands and never thought to try and form lasting alliances/truces, which most of us did, informally).
In the last 2-3 years most of our campaigns have been collaborative in nature, which is a lot of fun. (My wife is happier playing in collaborative games - like RPGs, than in competitive games).