Most of these guys hate Polyurethane, I doubt many of them use it much.
My method is relatively easy, and produces good results.
1# Sand the piece down to 320 Grit, until it's baby but smooth.
2# Blow all dust off with air compresser.
3# Completely wipe the piece down with mineral spirits, and let dry at least 15 minutes.
4# Using a 3" foam brush apply Helmsman Clear Gloss, at full strength.
5# Do not paint the poly on. Use a "New Brush for every coat".
6# Start in the center of the piece, go right to the edge, then go left passing thru you're starting point all the way to the left edge. Look to see that there are no dry spots. If there are repeat the stroke going left first. Slightly overlap each pass, working toward yourself. When you have reach the edge nearest you. Move to the other side of the piece.
7# All of this must be done farely quickly, with no fans or anything that speeds the drying process. The poly must have time to self level.
8# Leave it the hell alone, don't fix anything. "Sometimes the hardest part"
9# After 45 minutes to an hour repeat steps 4 thru 8. Don't worry about ridges or bugs or anything else. The next steps takes care of that.
10# Let dry for at least 6 hours, or up to 24's.
11# Using you're sander go over the whole piece with 320 grit. Do not use any downward pressure. Use you're fingers to test smoothness, you're only trying to level ridges, bubbles, and bug bodies.
12# Blow the white dust off, then wipe down with mineral spirits.
13# Apply the last coat and let dry for 72 hours.
From the looks of the piece in the picture, you should start at #11.
"Error of opinion may be tolerated where reason is left free to combat it"