agree with what bodhran just posted above. also, I will add, make sure before reading the cards, you have eaten and drank something. perhaps having a glass of water or something near you as well, while you're preparing to do the reading and start doing the reading.
reading can sometimes take a lot out of you energy wise. so it is important to always make sure you are in top form and beforehand- eating and drinking something that is grounding is also something you may want to consider.
grounding foods are typically things like meat, root vegetables, such as carrots, potatoes, radishes, onions, turnips, peanuts, beets, garlic, and so on. drinking a glass of milk is good too. it may help.