What are pre-writing techniques that help me start and most importantly finish what I am writing?

Do what comes to you naturally when you're preparing to write. There are many resources at your disposal, have fun trying them and see which method suits your personality. I have a brainstorming session but using key words, arrows, diagrams etc. I make sure the main message is in the centre of the page, then work outwards from there. You can send an email to yourself listing all the key points you want to put into your writing. You can use a dictaphone or voice recording on your mobile. Technology there to help you and you can always resort back to simple pen and paper. Whatever you do, keep it simple.

Each writer has his/her own "rituals" to get into writing mode. There is no such thing as a standard thing to do it. In other words, it actually depends on you.  It's a matter of attitude.