Relaxed 4a here. I've been on the boards for almost 1.5 years now and can defintely endorse the following:
1) What were the keys to your success?
Avoiding regular direct heat from curling irons and blowdryers
No damaging color treatments except for Sebastians Colourshines that seal the cuticle and provide clear coat or colored tinge (like a mixture of Ginger and Walnut)
Using protective styles like buns and via cute barrettes, clips
Trimming the underprocessed and burnt-up ends - I did this gradually since my hair was recovering from my Halle-mania days and I still wanted to keep some length but make it look decent. I also dusted the ends at home when I saw an especially frizzy patch. I salon-trim only twice a year now, but at those points, I am quite happy for the fresh ends.
Sealing my moisturized (curl activator or oil mixture) ends with a heavier cream (mango butter, protectiv breakfree)
Almost daily Conditioner washes helped me put moisture back in my hair (Nexxus Humectress, LUST, Neutrogena Triple Moisture Mask). Twice weekly or even weekly washings work just fine now because of daily maintenance regimen and products
Strong regular protein treatments (Aphogee) at the start to curb breakage of under-processed hair, and milder protein as needed currently (like Aveda Curesssence conditioner).
2) How often did you relax and how did you prevent breakage at the demarcation while you were waiting for a touch up?
I relax every 6 weeks (1" growth) but I watch my stylist like a hawk to make sure she does not overlap. Trying to stretch it to 7-8 weeks now that my hair is shoulder-length and buns actually are easy to make during those last few weeks before touch-up. I do not have to detangle and yank from the roots to the ends to make a style.
3) Any other tips that you might like to share.
Take care of yourself - get rest, drink lots of water, have a balanced diet with protein, good fats (olive oil, nuts), fruit, veggies, and take a multi-vitamin at the least.
Find a hair regimen and products that work for you and stick to it!! It may change a bit in the start as you bring your hair back to health but once u find your groove stick with it.
Get inspired -- search the net for stars with hair you like and make an inspiration album on your pc or your website. I also save hair colors, cuts and styles I like from the web and regular old magazine clippings. Make sure the pics show healthy, stylish hair of different lengths - so you can see the quicker in-between goals as well - ear-lobe bob, shoulder-length etc.
I hope this helps. Have a happy, hair-growing year!