Most people wonder what to do with their plants before traveling. It depends mainly on the season you chose to travel. You have to take into consideration the temperatures prevailing at the time as well as the span of time you will be gone for.
Some plant groups, like cacti and succulents will be more tolerant than the rest. Thick leaved plants will hold water in their leaves longer than thin and small leaves.
The best way is to collect all the plants you possess, put them in a bathroom, where humidity is usually higher than the rest of the house. Keeping in mind that natural light should be available. You can let the plants stand on big plates of gravel filled with water, to provide ample humidity to the plant.
If the period you are traveling is more than a week to 15 days (depending on the season), it is safer to have someone you trust water them when you are away.
Lots of other methods exist and are marketed with very little efficiency and success rate.