Former Scotland international Alexander was unveiled as Micky Mellon's successor on Thursday, five days after an FA Cup defeat to Aldershot cost the latter man his job.
The Cod Army lie seventh in the League Two table, two points shy of fellow play-off occupants Southend, but have won only one of their last six league games - a period in which Paul Sturrock's side are unbeaten with four wins and two draws.
"You've just got to put out a team with the right ideas and the right competitive edge to hopefully get a result for the club," said Alexander when acknowledging the limited preparation time at his disposal.
"That's all we'll be looking for on Saturday. It's going to be a tough game.
"I've obviously done my homework on Southend and they're a team on a good run at the moment with a really experienced manager."