A combination of the two - technique is important - how to comb, brush, relax, straighten, wash, condition, dry, style - we know using the correct methods are extremely important and make a significant difference in the health and look of our hair. Bad technique is death to healthy hair. Additionally, good products that work best for each individual's hair are equally important. The ingredients in hair products are most important.
I recently purchased a highly raved conditioner for co-washes because I wanted to try it. $4 for 16 ounces opposed to $54 for 16 ounces of my usual. The difference - water, water, water, water - thin watery conditioner which works okay, but it's not for me. I like my thick, rich, creamy moisturizing condition. In the trying of the new one, I found I used far more because it was so thin. However, there are others for whom this product works wonders. When we talk product, once we move beyond the basic necessary ingredients, we're talking personal preference.
One other necessary part is knowledge. Gymfreak (one of my favorite hair-growing scientist) made a post this morning explaining the signs of damaged hair and what is needed to counteract the damage. KNOWLEDGE IS POWER! Trials and error is all good, but nothing beats knowing the reasons why.