The best skill to raise your pay has nothing to do with upholstery. And everything to do with learning how to sell.
You might want to learn to sell your value, your skill, your knowledge, and your ability.
The next thing is to learn how to or get over the fear of asking for more money.
Now this is more for a business owner then an employee, but, but if the company you work for does this you can profit from the increase of income as well.
If you work for someone who is afraid to ask for more money, and or does not know how to sell the value of upholstery, then find a shop or build a shop that does. This is the main skill to success in upholstery or any other small business.
NOTHING is worst then working for someone who only knows how to lower price to get work. Run, Run, Run. Better to pull out your own finger nails then stay. You only want to work for the highest priced shops. Stay far, far, far away from the Walmart of upholstery. Find the Nostrums of upholstery. A shop that only wants to work with the well healed financially. I"m not saying only people with $200,000 sports cars, who live on the water, and vacation on the Riviera, but they should be up in the higher income earners. They have the money and will, WILL, spend it if you know how to ask.
How can I say such a thing? Well, I have learned from 30 years of struggle. Don't get me wrong, I worked hard, hard, hard but was poor, poor, poor for most of my career. I must like struggle. Some times I did not have money to by food for the family even when working 60 or 70 hours a week. I learned and those who don't, don't do upholstery for very long. I am just dumber then most I guess.