I'm looking to do a mosaic and need help

I find lots of idea's on the subject but not many talk about
how to start it.

do I need to draw out my idea?
then how do I apply over it without messing up?
I'm doing one on a large scale using large materials

I'm going to use rocks pebbles stone brick tiles
pavers what ever I can get my hands on the most and
do a mosaic pathway in my garden .
I dont need much help on the how to's but do need to know
how to design it . I'm not good a free handing so how do I follow
a pattern?

hope I'm making sense to someone , LOL

thank you