Stimson led his team to promotion from League Two last season but he insists none of his Wembley heroes are guaranteed their starting spots on the opening day of the season against Swindon.
He said: "I've told the players that last season is gone. It was great but it's history now and everything that happened last season counts for nothing now.
"It's all about what happens when they come back into pre-season training and I've told them that nobody is guaranteed a first-team place.
"The players have got to go out and prove their worth again, it's no good relying on what they did last season - that will be no good for the new season.
"The competition in training will be hard, in a good way, and that's helped us get where we are now."