If you do not train much before you leave, the worst thing you can do is try to walk the "standard" stages. Do not try to reach any particular destination each day (though you probably will have one in mind). Stop regularly. Tend to your feet. When they go bad, you will transition from discomfort to misery. Avoid that transition.
Get your footwear now, and be sure it is well worked-in. Do not take any standard advice on the size footwear to buy. Take the sock combination you will use, I recommend a silk or polypro liner and a medium wool or wool-blend hiking sock, and try on boots while wearing them. Get a proper fit with those socks, not one size larger or one size smaller! Get boots that fit; do not be focused on the size you have bought in the past. Some walkers experience foot swelling. To remedy that, I would suggest removing a layer of sock (or having lightweight wool socks in your backpack), not buying larger footwear, which will be larger regardless of the current size of your foot. When your foot is smaller, it will slide inside the too-large boot, and you will get blisters.
Pack very light. Leave behind everything that you "might need" except a first aid kit. You are not going to the wilderness; if you really need something, you can buy it along the way. You can wash every night, so one change of clothes is sufficient. Avoid style; go for utility, such as moisture wicking fabric, and pockets. Lighter colors are better in the heat of summer.
The one universal criticism I have heard from pilgrims who have seen "The Way" is that Sheen makes it look too easy. He bounces along from day one to day thirty. My bounce was gone within the first hour! You will be walking approximately a half-marathon each day for over a month. It is not easy, particularly if you do not take rest days.
Have fun. Go slowly. Buen Camino.