Wednesday made minor progress last term when finishing 16th in the table, two places higher than the previous campaign, and Bullen insists preparations have been going well ahead of the new term.
Conditions have been tough on a pre-season trip to Slovenia, but Stuart Gray's side have dug deep as the build-up continues towards their opening league game at Brighton on August 9.
Bullen told Wednesday Player: "We've got a very small squad at the moment, as everyone knows, but the sort of siege mentality that's building amongst them is fantastic. As coaching staff, it's probably the most important part of your team.
"We're probably a few players short of making a push next season, but the group we have and the spirit they are producing is going to stand us in really good stead. There's going to be ups and downs this season, we know that, but if you've got a tight-knit group, it saves you a lot of hassles.
"The year we got promoted when I was a player, we didn't have the biggest or best squad, but we had team spirit and I can see a lot of similarities with this group. After training, they are going home and having coffee together and there's a real group spirit."