I'll be growing my hair out for dreads for a while, any tips to make it lock better? - Dreadlocks FAQ's
If you're growing your hair out for dreadlocks and you have some time before it will reach the length you're waiting for there are a couple things you can do that will be helpful to locking later.
First off you want to make sure your hair is healthy and growing fast. Why wait longer than you need to right? See How do I make my hair grow faster.
One of the biggest changes your scalp will need to adjust to when you start your dreads is the change in washing frequency. If you're washing your hair every day now and you'll be washing it every 3 days later, that's a big adjustment. If you slowly increase the time between washings the oil that your scalp produces will naturally decrease. This will make the transition easier later on. The sooner you begin changing the washing frequency the more gradual the change can be.
You'll definitely want to stop using conditioners at least two weeks before you start your dreads and you can also begin using a residue free dread shampoo to allow the scalp to adjust and to ensure that the hair is as clean as possible for the backcombing. Here's some more info on things to do just before dreading.
Another thing you should do that's easy to overlook is make sure your job, school, parents, significant other, etc. are dread friendly. Maybe if you start working on them now they'll be ready for dreads when you are. You might find the Note to Parents, and Note to Employers helpful. You can also start working on lining up your dread party and decide who will do your sectioning before hand.
If you can have four people backcombing at once it will only take a couple hours and it will be much easier on you can everyone involved.