When following a bearing (i.e. attempting to walk in the direction indicated by the compass) do not just try to look at the compass and walk in a straight line. Even when trying hard to walk in a straight line on flat ground there is usually a natural tendency to deviate slightly (normally off to the right for right handed people) and in any case, the landscape is hardly ever nice and flat. There will always be reasons to deviate off your intended path, that clump of trees, those holly bushes, that mountain spur. Even with flat ground and good 'seeing' it is very tiring to continually check your progress against the compass.

The best thing to do is to look along your bearing (taking care that the compass pointers are aligned as best you can) and notice a landscape feature that lays along that path (e.g. "that large gnarled oak tree over there"). Then you can effectively forget about the compass and just make your way to that feature along the best possible root. Take regular sightings of the feature in case you lose sight of it during your 'detours'. When you reach the feature, simply take the same bearing again, (i.e. sight along the compass again) and repeat, looking for a prominent feature. With practice this is a very quick, yet still accurate method of travel. Of course it is not very effective in very poor weather conditions, at night, or in featureless landscapes, and there you will have to rely on regular (frequent!) checks on your compass. But for most situations it is effective.