If using Spar Varnish, of course the first is to sand smooth the area depending on what it is as to wood and if a stain is warranted. The key here is to thin the spar varnish so it will penetrate the fine pores and let it dry and then lightly sand after each coat. The method of application will be to your discretion but once built up, I then lightly sanded with wet and dry using 400 then 600 then 800 grit . At that point with a very slow speed buffer used a fine compound unless by hand to really bring out the shine.