Quarantine Your Houseplants
Quarantining your houseplants is simple and will save you a lot of heartache. You should always check for pests before buying but know that just because a plant looks clean, doesn't mean it is. By quarantining new plants you can avoid any nasty surprises.
How to Quarantine
Just put any new houseplants in a separate room from your other plants. If you don't have a room, you can always make a corner with cacti or other pest-resistant plants and quarantine new plants there. Leave the new plants in quarantine for a month, checking them regularly for pests. If after a month you haven't seen any pests or signs of them it should be safe to add the plants to your collection.
I have found it good to do a short quarantine with any plants that have been outside. Two weeks is enough if you check daily.