1. The most important thing to remember is the order in which you remove the fabric (exp. which piece you removed first, second, third etc.) and if you can't remember, then take pictures along the way or take notes to remind yourself of this process.
2. Use the removed pieces of fabric as a pattern to cut your new pieces. This fabric may be the nastiest thing on the planet so make sure you lay it out on the wrong side of your new fabric, so it doesn't get dirty.
3. Once all fabric is stripped, look at all the guts of the chair. Assess whether you can still use what's there and hopefully you can, because that would be the easiest. If not you may have to get a better cushion or padding. If there is anything structually wrong with your piece, now is the time to fix it, wobbly legs or arms, etc.
4. If there is any wood on your piece that will be refinished, do that before you start to reupholster (something I nearly forgot to do).
5. Reapply the fabric in reverse order that you removed it using a staple gun and pull tightly.
6. If you are using a nailhead trim, it's a LOT more complicated than it looks, even for someone who knows how to drive a nail. I have found that the best place to find nailhead trim is at home improvement stores, rather than at craft stores. It helped me to use needlenose pliers to hold the end and keep it in place while I used a tack hammer to gently nail it in
Gook luck. Send me pics when it's done, I'd love to post them.