Never dismiss your first impression. First impressions are the best impressions because they are completely raw, naturally spontaneous. First impressions are not complicated by the conversations, social dynamics, power plays or mind games that begin clouding decisions as relationships go on.
Learn to listen to your body. Intuition communicates to us not with words, but with physical and emotional feelings. If you feel nervous, uncomfortable, sick, bored, confused, exhausted or overwhelmed when you are with somebody, chances are that person is not a good fit for you. Do not ignore these signs. If doesn't feel right, it isn't right.
Forget reason. You do not have to have a logical reason for why you do or do not want to spend time with a particular person, so don't try to think your way into or out of a relationship.
See what is, not what you hope for. Sometimes we want so badly to be in a relationship that we allow our longings to blur all the glaring red "STOP!" signs. Make sure that you are not projecting your deepest hopes onto a reality that does not exist. It is better to see clearly and wait for a person that is right than to ignore what is wrong and hope that the wrong person will change.
Move slowly. Rushing into a romantic relationship too quickly and making yourself vulnerable before you have developed a strong basis for trust and understanding can cloud your judgment and diminish your capacity for hearing your intuition. Don't get entangled until you really know each other.
If you have the instinct to end the date (or a relationship for that matter), do it. Don't waste time or worry about being polite. If you have a bad feeling about the situation you are in, you have the right--and the responsibility--to remove yourself from that situation immediately.