The pair have now played together seven times in the Premier League for Villa but have managed just the one clean sheet so far - the 2-0 win over Swansea last month.
"It is getting better and better but we still need to improve," said Vlaar, who has joined up with his Holland team-mates for their World Cup qualifying matches against Andorra and Romania.
"We talk about it a lot together and I think everybody has to improve. If you believe you can then you can do it every day. It is a long way but we have to keep it up and move forward.
"The partnership with Ciaran is good but I think we have to better it, for the team and for ourselves. I think we can work on that every day and that is what we are doing.
"Communication can always be better and we talk to each other a lot about moments in the game, situations that have happened and what can happen in future. We always try to improve."