Avoid Planning the Entire Tour Yourself
Let someone else do the planning for you, as it may create stress before, during, and even after vacation. You don't wanna feel responsible for having to wait for a hotel room at 10 in the night, for some silly payment confusion, etc. And, later regret not handing it over to the agency (now knowing exactly what they charge the commission for!).
Do More Research
Read reviews by people who actually visited the place you're going to. Find out as much as possible about the place, lifestyle, weather, transport, certain peculiarities you would like to experience; all this before leaving, so you are equally well prepared for the happening and not-so-happening moments.
Don't Aim at Maximum Sightseeing
Keep it flexible and don't try hitting a 10/10 when you visit tourist attractions at a given destination. Plan a longer trip if need be, but don't rush yourselves. In fact, if you are really looking forward to 'relaxing', you should choose less crowded places and enjoy your way (basically avoid those long waiting lines for something like a 'light and sound show').
Plan for Emergencies
When traveling with kids or elderly people, make sure you have a plan in case of a health emergency. You may wanna pack the luggage accordingly; that includes not just medicines, but something like medical history. Also, keep enough time to waste/spare a day or half so that they can take a break.
Decide Rules for Group Travel
Traveling can get a little difficult with strangers or acquaintances. Know that everyone will have a different preference, and let that be accepted as rule. Let each one choose how he/she wants to go around the place, and probably meet up for lunch or dinner somewhere later on. You might even end up going to the same places at the same time, and like it that way.
Avoid Taking Work Along
This requires reverse-planning, and great execution too. Plan a vacation at the right time, which means, at the time you can afford to take a break from office. Give your boss or colleagues a plan for your absence, and accordingly finish your pending tasks before you leave. Decide when, if you must be in contact with them, and keep it minimum. Remember why you're on a vacation!
Leave Behind Your Identity
Simply get out of your shoes and move into a new world to refresh yourself. Keep all your worries as a boss, employee, businessman, or housewife at home. Be like any guy or girl next door. Try seeping in the ways of the destination, and don't go upset at how bland the food tastes. Expect less and try finding fun in the moments you live away from routine.
Plan Well for a Post-vacation Comeback
We request you to keep a day or two for yourselves before you go back to office after a week-long trip. Take time to adjust. Avoid scheduling important meetings or conferences right on the first day you join back. Get in touch with what you missed out on. Discuss with your colleagues about what happened in the meanwhile. And, go a little slow with yourself initially, for a faster and productive comeback.