I strongly agree with S & L. Using just the watch and compass is the best way to improve your basic nav. Other exercises are to estimate the 2000' wind from surface wind reports and use this to calculate drift and groundspeed for your intended track. This is a very valuable cockpit skill to acquire for planning and flying a diversion. There is an excellent booklet called "Diversion Planning" by Martyn Smith available from the usual mail-order pilot shops. It only has 15 pages but its the best of its kind and the subtitle says it all: "How to Navigate around the world using a stopwatch and a pencil".
QNH