The Two-Strand Twist Method

This is probably the most common loc start-up method.

The hair is parted/sectioned off as desired. With each section, you will divide the hair into 2 strands and twist them from the roots right down to the end of he hair (like rope). Some loc-ers start this same process by braiding the hair at the roots to keep them tight, and then twisting.
Pros Cons
This is a method that is very easily done at home with little-to-no cost involved. It looks very neat right after completion, gives you an almost loc-like look very quickly and withstands coming undone throughout washing and styling. If you choose to braid the roots, you will probably be able to tell the difference between where your locs were braided vs. where they were twisted-although probably only up close.