PEC film cleaner works quite well if you don't have a lot to do. Just remember that many of these solvent products are unsafe to breathe or often even have skin contact with, so decent ventilation and nitrile gloves are a must. De-Solv-It is nontoxic and more affordable than PEC or Goo Gone, but works slowly and is a distinct irritant to skin and the respiratory system; so religiously wear gloves with it too, or you might find your fingers quite dry and itchy the next day, and use good ventilation why it slowly evaporates - up to 24 hrs. Usually a soak time of 20 min or so works with masking tape residue, provided its not a lacquer resistant masking tape, which would require some scraping first.
De-Solv-It is citrus based; but with all the solvent varieties you need to be aware of their serious flammability. Lab grade 99+% pure methyl alcohol works especially well, but evaporates quickly and is darn expensive. Ordinary hardware store or drugstore denatured alcohol has a lot of water in it, and is generally worthless in these instances. Acetone and lacquer thinner will attack vinyl and many plastics. Naptha and turpentine have been banned from paint or hardware stores in some States due to smog regulations, while the art store varieties tend to be terribly overpriced.
Softened adhesive guck should be removed with a soft nylon Scotchbrite pad or repeated paper towels. Anything you miss will remain sticky and just have to cleaned off afterwards anyway.