Practice negotiating for cheaper coffee or fruits at the farmer's market, where you have nothing to lose. Research, understand and internalize your true value to employers, business partners, landlords and all others you deal with. Be confident about your capabilities and set your limits when you go in to negotiate. Come in with concrete and measurable facts about what you've done, on what budget and time frame, how much money and time you've saved the team and company. Practice with a coach or a no-holds-barred friend beforehand.
Before I ever negotiated for anything, I was hampered by all sorts of insecurities and hidden scripts in my head that were passed down from parents, siblings, friends and cultural vectors. When I met my wife, who grew up in Morocco and negotiates for a living, the paradigm was turned upside down. In Morocco, NOT to negotiate is insulting and looked down upon. Locals always know the true price and the "acceptable" margin.
EVERYTHING is negotiable.
I slowly untangled my own hangups about negotiation, learned to understand my own true value to an employer or business partner or vendor in each case and started practicing with negotiation in a Moroccan bazaar, where there was absolutely nothing to lose.
With time, I successfully negotiated a full-time offer with benefits after being offered a contract. At that job, I ended up negotiating a 23% discount ($45K off) on financial management software - far better than expected for a company of our size. I then negotiated a cap of 1% on rent over 5 years (saving the company $17K). At another job, I negotiated $10K and better benefits/perks higher before starting. Since then, I've negotiated big discounts (20% or more) on everything from moving company expenses to rent, consulting rates, car rental fees, credit card fees, hotel chain points, coffee and all sorts of other large and smaller purchases.
After a while, developing a negotiation mindset has not only saved (and made) me tens of thousands of dollars, but also given me confidence and competence that are priceless. It's a snowball effect that consistently opens up big savings, perks, freebies, extra points and other "hidden" benefits.
The rule with negotiation is simple: If you don't ask, the answer is always no!