From what I can gather from Internet research so far:
You should only attempt to varnish any surface after fairing the wood, with ultra fine sandpaper, so well that it's almost worn through completely. Oh yes, and you must sand with the wood grain or else the wood will end up scratched.
The workplace must be warm and completely dry. Not too hot mind.
Also, you should scrupulously clean not only the workpiece to be varnished, but the whole room to ensure the place is completely dust free before starting. It's best to use white spirit for this.
After cleaning, it's best if you can leave the workplace hermetically sealed, and undisturbed, for at least two days, so that in the unlikely event there is any remaining dust, it settles completely.
To varnish, it is important to wear a full body set of coveralls, which are both dust and lint free. Adequately covering for your hair is particularly important.
The varnish should be gently heated to 21.5 degrees centigrade, but no more than 23 degrees, so it flows best. A warm bath works well here.
To use it, the varnish should be decanted into a suitable container, to prevent contaminating the varnish tin with that used brush.
Then, and only then, should you apply the varnish, using a brush with bristles made from the underbelly of virgin Japanese badgers.
Use long, flowing strokes and keep to the recommended coverage per square foot, or metre, depending on your preference.
The varnish must also be stirred continually during the varnishing procedure.
It's best to start each new coat with a new brush for that perfect finish.
Of course, while varnishing, you should always move slowly around the area you are working in, to avoid raising dust, and you should not allow anyone else anywhere near until the varnish is completely dry.
After varnishing you have to sand everything off, with even finer sand paper, and then start again with the whole dust free thing.
Do the above several times, of course, to get the best possible finish.
Incidentally partially used varnish tins should be stored upside down, and at an angle, to prevent leakage or 'stalactites' from forming.
Hmmm, this is Lady Jane we are talking about. A more pragmatic approach is required here methinks.
Here you see the results of my first ever attempt with varnish - obviously I didn't heed any of the advice gleaned from the Internet here.