A new pair of leather boots needs to be waterproofed; and an old pair needs to be re-waxed at least once a year. I just waterproofed mine last weekend because spring is coming up and down here in the southern US we get lots of rain plus spring and fall are usually when I like to re-wax. Chances are if you spend enough time in the mountains most anywhere during any season you will get wet at some point. Keeping your feet dry is just one part of the whole equation. Keeping feet dry and sometimes even warm is a science, but here I'm just going to go through the steps I take to insure my leather boots are waterproofed. By waterproofing leather boots at least once a year, depending on the amount of usage and weather conditions, you can prevent most moisture from ever getting a hold on your boots; it will bead-up and roll off them much like a car that's been waxed.
Make sure your boots are clean and dry. Get some waterproofing wax for leather at your local outdoors retailer.
Put some wax on the boot. and rub it in real good with your fingers. Spread the wax around so there is no build up, but make sure you are getting a good thick coat on the leather.
Use your finger tips and the extra wax on them to stuff wax into any seams. I like to make sure all the seams are waxed extra good because those are the kinds of places water will try and seep in.
Keep adding wax as necessary until the boot is finished. Relax and take your time because the work you put in now will pay off later on the trail when the boots get wet. You can compare your finished boot to your unfinished boot. A finished boot will look something like this.
Again check all the seams to make sure they got a good coat of wax in them. In these next photos you can see the difference up close after waxing around the seams (note wax build-up inside on the tongue of the boot, another area of concern against water).
You're done; now just let the boots dry for a couple of days.