Albion, who have lost to Newcastle and Manchester City in the past week, entertain Norwich at the Hawthorns this Saturday.
A trip to Cardiff and a home game against Hull City follow before Clarke heads to London for a double-header with Spurs on Boxing Day and West Ham on December 28.
New Year's Day sees the Albion return home to entertain Newcastle and it's to those five games Clarke is looking to for pointers towards the remainder of the campaign.
"This is a key period for everybody at the club," said Clarke, whose side are currently 13th place in the Premier League table with 15 points from 14 matches.
"We've had some really good performances, but haven't picked up the points we needed and now we're going into a period where we've lost a couple and that can always happen.
"When you're in a good moment you have to pick up the points, so now we're a little behind where we wanted to be which we have to address that over the next few games, starting Saturday.
"This time of year - December and January - you will know after that period whether you will be fighting at the bottom or trying to chase those at the top.
"So that's what we have to do over the next few games, define where our season is going to be."