After years of promise, Smalling is finally fulfilling his potential under the guidance of Van Gaal, with the 25-year-old yet to miss a match for United in eight matches across the Premier League and Champions League.
Smalling, who has captained United in the absence of Wayne Rooney and Michael Carrick this season, has arguably been the team's best player in 2015-16.
The former Fulham centre-back believes he is benefiting from Van Gaal and the Dutchman's training methods in an interview with Sky Sports.
"I think he [Van Gaal] has [improved me], all the coaches I've worked with, especially Louis van Gaal, have helped me," Smalling said ahead of Sunday's trip to Southampton.
"We work hard and tirelessly on the training ground with our tactics, we do 11 versus 11's a lot so we know our positions and our roles down to a tee.
"The repetition has really improved my game and a lot of the other players as well.
"The manager said at the start of the season that once you've been with him for six months and got used to the repetition of drills, the tactics and you know your role that we will get better.
"There has obviously been a lot of ins and outs and, as a group, we've stayed very close-knit.
"Whoever comes in knows their job. We have the training routine and the philosophy of the manager so every player knows what he wants and what he expects of you on the pitch.
"It's very clear to us as players what we need to be done come matchday. We started this season a lot better than we did last season and we can see an improvement."
Smalling, who suffered thigh and groin injuries last season, added: "It's nice to know the manager has got that trust in me and I hope to deliver.
"I've really enjoyed it. Considering how last season started, when I was stop-start and didn't pick up until November where I got a consistent run of games.
"So to be able to start with a clean bill of health and to have the manager's faith has given me the confidence to kick on and make sure I have a full season and justify my place."