Never update your contesting software the day of the contest....... "Software surprise" is not needed during a contest.
Never assume your contest station is running great just because it was last time. ..........Give the station a workout a few days before the contest.
Never update the rigs firmware just before a contest.......firmware glitches will throw your contesting off.
Never forget about the family during a contest weekend.......an hour away here or there can be a refreshing break.
Never get upset and frustrated......it's a contest have fun, know from the outset there is going to be poor op's out there.
Never think you are NOT going to get board at times.....there will be slow times have other things planned.
Never forget about non-contesters and respect mode allocations on the bands.......it's not intentional most times we just get carried away.
Always make sure the YL's "honey do" list has no outstanding promised items for that weekend.
Always understand that things never go as planned.
Always have some exercise, break times and eating times planned, a crock pot menu is a great way to have good dinners with very little work.
Always use headphones (especially CW contests) it may sound like sweet music to you but to the rest of the family (pets included) it's NOISE!!
Always have some goals for the contest.....and understand they can change.
Always make sure you are comfortable....cool in summer, warm in the winter, good chair and operating position just to mention a few things.
Always investigate if other major contests are going on the same weekend.......it can get frustrating when two stations from separate contests are giving exchanges neither can understand.
Always read and understand contest rules before the contest..........self explanatory.
P.S.....please leave your comments with more includes or avoids