Decide how tightly escorted you want your trip. Some tours provide the escort during transports and your itinerary in between locations is up to you. Others plan every last detail of your trip so you're virtually never on your own.
Find a reputable touring company that's experienced in organizing escorted tours for seniors. Remember, price isn't the only consideration when measuring competence. You want a company with a solid record with past customers, so ask to see a few references.
Consider booking a tour out of season. There are many benefits to seniors who do this. No matter the destination, going there out of season means it's probably going to be less crowded and less hot (or cold) and less expensive than during peak season.
Be very clear about what is included in an escorted senior tour package, no matter the destination. Consider items such as meals. Are wines and other alcoholic beverages included and will you be able to order anything you choose from the menu? Find out if there are entrance fees for sightseeing, tips for serving personnel, a "group donation" for the guide, and any other items about which you would normally stay unaware until it's time to cough up some cash.
Research beforehand the area you'll travel and see if there are any festivals going on while you'll be there. Some escorted tours do allow clients to choose evening activities.