The Terrors won their third Ryman Division One South match on the spin on Monday with a 2-1 win at Carshalton Athletic, and Tanner is demanding more of the same.
He said: “We controlled the game at Carshalton and could've been three or four up by the break.
“I warned the players about failing to kill the game off and, despite being two up with 10 minutes to go, we became sloppy and allowed them back in it.”
Striker Sol Pinnock opened the scoring on Monday and defender Jordan Cheadle converted a second-half penalty to seal all three points, but it was the missed chances that weighed on Tanner’s mind most heavily.
He said: “Last season we only had a squad of 16 players but now we have some healthy competition, particularly for forward positions.
“Those that start games know they must play well and take their chances otherwise there are others chomping at the bit to be involved.”
His men host Three Bridges in an FA Cup preliminary round match this weekend, an opponent the Terrors beat 4-0 in the league last Saturday.
“We struggled in the first half against Bridges but eventually came good, so we'll approach the game in a similar manner but look to start brighter,” said Tanner.
“I want us to progress as far as possible in all competitions so it maintains a winning mentality.”