get a good ski boot or snowboard boot fit in a store

What to bring and wear
ONE THIN pair of ski socks (two pairs will cause circulation and friction problems). Custom Footbeds (if you have them). Wear shorts or loose pants that you can pull up to your knees.

Consider
Current skiing ability, history and aspirations.
Favorite trails & conditions to ski. Current boot model - likes and dislikes.

Proper Sizing
Ignore the size of your current ski boots or shoes. Many boot companies have unique sizing and each will fit you differently. Use the company supplied fit sizer or focus on the shell fit. This will accurately tell you your size in whatever brand you choose.

To shell fit
Slide the liner out of the boot. Place your foot in the shell only, with your toes just touching the front of the boot. Two fingers width space behind the heel is just about too much, less than one is too little.

After shell fit
Place the liner back in (with your custom footbed if you have one). Boot should be snug all around your foot, without pinching or hot spots. Initially you will feel your toes at the end of the boot. When the boot is buckled and you flex forward, your toes should come off the front comfortably.

Now what?
If the initial fit is painful - take it off and try another! If the initial fit is comfortable, wear the boots around for at least twenty minutes. If after that time, it feels great, buy it! Now that you have a boot that fits, you can fine tune the flex, stance and other adjustments to suit your preferences.