Backstay Tension
Light to Moderate - no tension.
Medium to Heavy - adjust as needed.
Traveler
Centered all times.
Mainsail Sheeting
In heavy air - sheet hard and keep an eye on the top telltale to ensure that it flows and you are not stalling the mainsail.
In heavy air - tighten the boom vang to induce mast bend down low and ease the mainsail in the puffs.
Downwind - always make sure your battens have popped to the proper side when you have completed your gybe. In heavy air, you will need your crew to ease the boom vang an inch or two when sailing downwind.
Jib sheet
Upwind - adjust the jib sheet so the leeward sheet sets square to the boom.
In breeze - sheet in an inch or two tighter to get more leech tension.
It is best to slightly over tack so you tack into the jib stay sag. Not fully completing a tack will prevent your boat from accelerating properly.
In light to moderate wind, you will have more jib stay sag. As the wind builds and you are sheeting the mainsail harder and harder, the head stay will flatten out. The head stay will flatten more as you increase the back stay.
Harbor 20s were design to perform best in the moderate harbor breezes of Newport Beach. They tend to be underpowered in light wind and become overpowered when the breeze is on.