Aberdeen were held to a goalless draw by Hibernian on Sunday while Saints lost their last game 3-2 at Motherwell despite dominating for large spells.
Lomas said: "It has been our Achilles heel all year, not taking the chances.
"We have to keep creating chances and hopefully that will rectify itself.
"We need to keep believing, keep creating chances and we'll take them, and obviously be tighter defensively than we were."
Niall McGinn missed a penalty against Hibs and Brown is looking for more urgency in front of goal.
Brown said: "I felt we played well on Sunday but could not get the goal we required. You cannot get a better chance than from the penalty spot so when you miss a spot-kick you think it might be one of those days, another of those 0-0 games that we had at the start of the season.
"I was disappointed with the players when they were stepping over the ball, making an extra pass when they could have got an early shot away.
"The lads are aware of that and we talked about it when we watched the video as we always do.
"Not enough of our shots troubled the goalkeeper. I was also concerned about the quality of our free-kicks so that is something we will be working on."