Long was part of the Reading side that led 2-0 at half-time against Villa in the FA Cup quarter-final two seasons ago before John Carew inspired an incredible comeback as the Royals eventually fell to a 4-2 loss.
"Getting relegated with Reading was a bad day but that Villa cup defeat was up there as one of the biggest disappointments of my career," Long told reporters.
"If Reading had won, it would have been the first time they had got to the cup semi-finals.
"At half-time, we were told to go back out and see out the first 15 minutes of the second half at 2-0. Within 10 minutes, we were 3-2 down.
"At least Villa haven't got John Carew now. He was ridiculous up front with his strength and touch that day."
The Republic of Ireland international was responsible for Reading's two goals that day and hopes that if he can repeat his personal performance, a different outcome will follow.
"I learnt a lot from that game," he admitted. "It showed the sort of club that Villa are and we've got to be right on our game to come away with a result this weekend.
"Hopefully I can emulate the two goals again and put things right.
"But, if we do take the lead, we've got to be as resilient as we were against Wolves at the weekend and see the game out."
Long added that West Brom would be expecting Villa to come quickly out of the blocks after suffering a heavy defeat at the hands of Manchester City last weekend.
"It is going to be tough," he said. "It is a hard place to go. Villa have a lot of history there and they are a great side.
"They have started very well but lost 4-1 at City so will come out all guns blazing trying to put that right and prove themselves.
"But, I know if we perform as well as we did against Wolves, we can come away with all three points."