The result was the Cottagers' second victory in the last three after a win away at Ipswich Town was followed by a draw with Cardiff City.
"To be a more serious and competitive team we must improve, this is not enough," Jokanovic told reporters.
"I am not satisfied with our performance, I am satisfied with three points but today we were under a big risk, we didn't finish what we needed to in the right moment and this kind of risk you can pay an expensive price for, which we have paid in the past.
"We must be braver, more solid, more adult, if you want, in some situations. In football, during 90 minutes there are always some moments where you are not comfortable during the game where the other team dominates you.
"This is not enough for me, this is not enough for our supporters and this is not enough for my team too. We must work harder."
Fulham face a trip to Burton Albion this weekend before hosting Middlesbrough at Craven Cottage.