The blood test for herpes detects antibodies in the blood. The antibodies are not present for a few weeks after the initial infection and up to 3-4 months. The benefit of getting a blood test now and later would be to tell when you got it. If you are negative now, but positive in 4 months, then you can deduce that you just got infected.
They say 50% of people have type 1 oral by age 12. They get it from kissing there relatives when they are young or chewing on toys that other kids were chewing on, like at day care. So it's pretty hard to avoid everyone that is positive if you actively date and kiss people.
Also if you are concerned, avoid touching your mouth, then touching your genitals or other body parts (eyes, etc.) because during an initial infection your body doesn't have antibodies and it's easier to spread it to other places. Once the antibodies build up, that is very unlikely.
You may want to check out this website and message board:
Herpes - Sort the Facts from the Fiction
Herpes & Cold Sore Support Forum