Dr Graeme posted these help videos on YouTube to help others develop there own line following EV3 robots. Follow along with him as he builds the line following robot. Remember your robot is different then his so your values will be different then his. Speed can be your worst enemy  in this project. Yes you want to follow the line as fast as possible but you don't want to over shoot the line either. You will be spending a lot of time dialling in your program to achieve the fastest time. Good luck.