I’m not an expert - its all about the observing!
There are some fantastic books on natural navigation that give ideas and clues about common indicators to determine direction. However most of what you need to learn can be done by getting out to a favourite place and spending time looking, observing and trying things out. Growing up on the southern side off the isle of Wight you could often tell at a glance how long it was until full darkness, when the rain was going to arrive or due to the consistent prevailing wind where the south west was even on a cloudy or windless day (North East leaning hedges and bushes). This was all knowledge picked up from being out and about as a child and a young man den building and outdoor playing, fishing, walking and camping. During the last few years of teaching navigation in the New Forest some common patterns have been observed that occur most of the year and across most of the woodland and heathland in the forest.
Out and about in January
The best place to start is at the start! - Park up or walk to an area and try and work out which way is south or north using the clues around you or cheat with a compass (most people have one on their phone). Look around at the tress, plants and even go for the obvious one, the sun. Look for patterns, form your hypothesis and then go and test it and check it.
This time of year the broadleaf trees are bare of leaves and it is fantastic time to look at the branches coming out of the trunk and make a note of the direction and shape of the ones that face prominently south. Standing and looking up at the trunk the longer and thicker branches with branches spreading out from them are the southern ones. Stand with your back to the trunk looking up with those branches each side of you, you are likely to be looking south. Have a go and see what you discover.
Ivy shows the way north
Well it does usually, sort of… If the ivy steam clearly starts on one side of the tree and then swaps to the other (with a clear turn in the lower stem) then it does start on the north side, more or less. If the ivy stem stays on the same side then that is usually the south side anyway; which ever side it starts from as the plant grows up the tree it gets to the southern side eventually.
The strongest storm winds blow from the south west. The toppled trunks and root balls consequences can often be found in the forest and it follows that the majority will have the trunks and tip of the tree pointing to wards the north east and the roots will be towards the south west.
Check out this YouTube video of my first practice using natural navigation techniques in the New Forest. The video was a spur of the moment thing so all handheld using the https://youtu.be/aA3bdsCXniE