PID controller and motor control

I have PID line follower Project and im about to set the Kp value. i dont know what Kp value i should go first.
is there a method determining the value of Kp ?
can any of you guys give me solution or suggestion ? im a newbie btw. thanks

Do you know the open loop gain of your control loop and its response poles and zeroes?
If not use trial and error (very common way to tune PID loops).

There are numerous resources on the net about tuning PID loops.

PID controller - Wikipedia