First off...go out and buy the book: STICK AND RUDDER , read it and fly it.
Now...I have lots of time in the PA28 Series...but there are many versions of the PA28, so always state the whole designator like PA28-140 etc.
NOW, WITH your instructor, go up to a safe altitude, configure for landing and STALL it...note the speed where you really stall.
Go back and fly the approach at 1.3 times the above speed. aim for touchdown speed no lower than 1.1 times the stall speed. this for favorable , no wind conditions.
NOW, go to a quiet room, do a weight and balance calculation, determine exact weight at start of approach, look for calculation information for stall speed/Vref calculation for your exact weight...it may be different than the POH, because the POH usually gives speed for MAX weight.
I do recall the PA28-161 had an approach speed of 63 knots( from memory 30 years ago)
also look up speeds for short field landing.
and DO read: STICK AND RUDDER