1. Read a brief overview of Montessori
Dr Montessori's Own Handbook by Maria Montessori is the best place to start in my opinion because it is a quick read and an excellent synopsis of Montessori. There are some lovely anecdotes from the earliest Montessori classrooms, which give a picture of Montessori in practice.
An even briefer overview of Montessori can be found on my website.
2. Read an introduction to the materials and activities
Elizabeth Hainstock's two books: Teaching Montessori in the Home: The Preschool Years and Teaching Montessori in the Home: The School Years are condensed Montessori manuals. They do not include as many activities as other manuals but this means that they can quickly be read from cover to cover, giving the reader a view of the Montessori progression, which I think is valuable to get early on.
3. Support groups
Playschool6, Montessori homeschooling discussion.
Montessorimakers, discussion on making Montessori materials.
4. Observe the child and start making and collecting materials
Observe your children. What are they interested in? What absorbs them? What causes them annoyance? What activities in their daily life are they striving to master for themselves?
Start preparing materials for Montessori activities. Any Montessori activity you think your child will be attracted to. Maria Montessori stressed that although her activities are designed in logical sequences, building on each other, the best order in which to introduce them to an individual child depends on the child.
Montessorimakers is a great source of information on different ways people have made Montessori materials.
There are a number of websites offering printable Montessori materials for download.
5. Start presenting Montessori activities
If the child enjoys an activity, allow them to explore it and work with it freely; then, over a period of days and weeks, continue with the activities that follow on. If the child is frustrated, put the activity aside for a while; try something easier next time.
I have found that doing Montessori at home means the adult needs to initiate more activities than a Montessori teacher in a classroom might. In a classroom, the children get ideas for work from watching each other. At home, the adult getting an activity out and working with it attracts the children to the work and reminds them of the choices available.
6. Observe the child and the environment and remove obstacles
Anything that hinders the child ... tv; playstation; toys that are just getting in the way and not satisfying the child; clutter. There might be more specific obstacles: a bulky jacket that makes it hard for the child to make full use of their hands; the child enjoys sweeping up spills but can't open the cupboard where the brush and pan are kept.
7. More information
Check out the Manuals, Books and Links page on my website for more exhaustive Montessori manuals than Hainstock's books.
One of the books that has helped me most in my homeschooling is Maria Montessori's Discovery of the Child.
Chapter 27 of The Absorbent Mind by Maria Montessori is all about the teacher's role in a classroom of preschool children new to Montessori.
A note on reading Montessori manuals
Montessori manuals (often called albums) give step by step instructions for presenting activities. I often find the steps hard to follow if I just read them. I have learned to read Montessori manuals with the Nienhuis catalogue open beside me so I can see what the materials look like. If I have the materials for the activity or similar materials, I have them beside me too, so that I can follow the steps with the materials. If I don't have the materials yet, I use pencils, paper and scissors to make makeshift materials as I go along.