After suffering a pre-season hindered by injury the former Shrewsbury man made a goal-scoring start to the campaign, but admits he has been disappointed with his recent showings against Barnsley and Doncaster.
"I had a chat with the manager this week about working, it's been documented I didn't have a great pre-season," he said.
"I think last week I didn't work as hard as I normally can and the manager said when I don't do that people notice.
"You've got to be honest. If you don't look at your performance and criticise it then you'll never come out the other side.
"I think anyone who was here today will see a drastic improvement from Tuesday."
City are up to fourth in the Championship after securing their second away win of the season, and despite dominating for long periods against North End, Holt says at times it felt like the victory might not come.
"We were unlucky, we had a lot of opportunities. It didn't seem to go our way," he added.
"You think 'is it going to one of those days again?' We've got a resilient side in there who want to win football matches.
"We don't go anywhere for a draw, we go to win games. It's great we got the 1-0 and it will give the defence and [goalkeeper] John Ruddy a great boost getting a clean sheet."
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