Write a mission statement for the season. The mission statement will contain the season's main objective. For winning teams, that objective usually means challenging for a trophy, or winning a league. For losing teams, though, the season's objective might simply be scoring one goal all season, winning one game, not tying one game or conceding less goals than the season before. Whatever the objective, write it into the mission statement and have all players buy into it.
Work on defense only. Choose a defensive formation that will reduce the number of chances against you. Play strong players in the back, preferably those with a good foot. Put one or two speedy players at forward positions for counter attacks. Play bunker defense and ultra-direct soccer. Not every player can be a finesse player on the ball, but every player can learn how to defend well.
Become good at set pieces. Every team, no matter how bad, will gain a set-piece opportunity at some point in a game. This could be a free kick, a throw in or a corner. When players see success or near-success from set pieces, it motivates them to keep playing in a manner that increases their chances of gaining set pieces. Teams that score from set-pieces will usually have one to five chances to score in a game. For a losing team to score on a tough opponent from a set piece will be all the motivation they will need to work hard for the rest of the season.
Focus on performance rather than result. If the focus is taken off the score board and placed firmly on the players' efforts on the field, it will often be the case that results themselves, by default, will improve. When players see their hard work paying off, they will become, in turn, motivated to work harder. As long as the emphasis is always on the method of playing and the work on the field, and as long as the score is treated as an afterthought, players on losing teams will usually find reserves of motivation they never knew they had before.
Stay positive, even in the face of adversity. Whether the seasonal goal is to win one game or not have the worst defensive record, all plans will come across a bump at some point. It is important to stay focused on that season's mission statement in situations like that, and to stay positive. Staying positive is an important factor in consistently motivating a losing team to become better and tougher to play against.