1)In my experience often don't fly what they planned, when they are supposed to be on a heading of say 270 they will often consistently fly 250-260 or something like that.
2)Students generally look for features that are too close, keep the big picture in mind, look for bigger towns and bigger features that are further away and pick a marker on the horizon and fly towards that, the heading will then be rock steady and adjust as required.
3)Mark everything you need from the flight log onto the map, headings, times, frequencies etc, then you don't need to look at the log unless you want to.
4)Reduce work load, Leave the lever at a set power, maintain altitude with cyclic only, only when airspeed is consistently 5 knots over/under target should you adjust power.
5) use the elapsed time to recognise how far along the line you should be which should be pretty accurate if you remain at set power and altitude.
6)read from map to ground as mentioned earlier - reduces workload