There are a couple things you can do.
-Lead by example: When you have a number advantage, go offensive
Learn how to use the mission maker, and make some missions that folks will join (ie, don't make the mission an hour long thing) The battles flow fast so make a fast-paced mission. Your mission building skills and the success there within will inspire others to do the same, I can remember a time in Knitland where I was the only one making missions, now we have a flock of excellent mission makers, 24/7.
-When you are low on numbers, go defensive, with small offensive missions
Continue making missions for smaller numbers so you don't strip your fields of needed manpower for defense. Make some missions that will draw the heat of your front lines, allowing those on defensive to get the upper hand and not lose their fields.
I could go on and on with this subject, but thats a good start for you. Never depend on others to 'do the action', you must do it, and promote it, and then lead them.