The following coating schedule for applying varnish is offered as guidance, not gospel, but following it will nearly always yield a head-turning finish.
Coat 1 — Thin about 50% with the specified thinner. This is the sealer coat. Allow to dry overnight.
Coat 2 — Thin 20% with specified thinner. Do not sand sealer coat before applying coat 2. Let dry 24 hours.
Coat 3 — Thin 10%. Apply over coat 2 without sanding. Let dry 24 hours.
Coat 4 — Sand coat 3 lightly with 220-grit paper. Apply varnish full strength. Allow to dry over at least 2 nights.
Coats 5 & 6 — Same as coat 4 except sand between coats more heavily to "plane" the surface smooth. Flat surfaces may be sanded with an orbital sander.
Coats 7, 8, & 9 — Sand by hand with 320-grit paper between coats. Apply varnish full strength, taking extra care to avoid runs and sags. Allow each application to dry over at least 3 nights before overcoating.
Coats 1 through 6 can be your finish varnish or a less expensive formulation, but do not use hardware store varnish. General purpose varnishes are typically too brittle for marine use. In hot weather coats 4 through 9 may require a small amount of thinner to keep the brush from "dragging."