The 56-year-old has masterminded much improved displays from the Scots since taking over from Craig Levein, and victory over Croatia finished the campaign on a positive note.
"It was great to see the composure of the players," Strachan said, after goals from Robert Snodgrass and Naismith sealed victory.
"We weren't sacred of the Croatians, who have some talented players, and was pleasing to see the players do what we have been practicing in training."
Strachan was particularly pleased with the contribution of Naismith, who collected his 25th cap on Tuesday night.
The Scotland boss said: "There was good football out there and there must be special praise for Naismith, I thought he was fantastic.
"It gives us all great optimism and I think we can add to our squad.
"We'll add technical ability and all the rest to the squad, but the players' heart, concentration and determination was great."