Vacuuming - once all the sanding is done, hire an heavy duty vacumm cleaner to remove all the sawdust. These are stronger and built to remove the sawdust particles faster and more effeciently than a domestic vacuum. Don't use a domestic vacuum - you will damage it with fine sawdust particles. Get all the sawdust out of the gaps between the floorboards, because once you apply lacquer, the dust will get lifted out onto the surface via the next brush stroke. Once you have finished vacuuming, use a damp mop to remove the final traces of sawdust.
Applying the lacquer - read the instructions. Use a brush for the edges and a short hair roller or floor pad for the main floor. Pick a good quality wide brush as these don't lose their bristles. If you use a gloss laquer ensure the final sanding pass over the floorboards was done with at least 120 grit sandpaper, otherwise the gloss laquer will show up all the imperfections. Satin or Matt lacquers are much more forgiving when hiding "issues" and imperfections. Apply the lacquer along the grain, from one end of the floorboard to the other. The goal is to keep the edge of the applied lacquer wet. For each session, if using an oil based lacquer, I would recommend using a new roller and brush, providing the bristles are not stuck together. Cleaning the brush is messy so you might need to buy a few of them. Only apply enough lacquer on your brush or roller so that you can get an even consistent spread - several coats are better than one thick one.
In the picture below, you can see the unique nature of each floorboard - one even looked like it had leopard spots!
Starting point - start at a corner and work towards an exit point, so that you can get out.
Smell - leave doors and windows open. If working at night you will need nets otherwise the insects will get in, especially at night time when they get attracted to the light and end up stuck to the floor. P
osition a fan so that it is blowing the air out of the room. A mask may help, but you need to work fast as the lacquer stinks. After the all the lacquer has been applied, you will need to leave the windows open for up to a week to allow the air to circulate out the fumes.
Recoats - read the instructions. Drying times will vary, based on the product, humidity and temperature. Make sure after your first coat that you have enough to start and finish the next coat.
Don't work in extreme heat, as your roller/brush will dry out.
In the picture below, I used the following satin oil based polyurethane lacquer which you can get from Bunnings.