How does one ask for a raise without sounding desperate or an asshole?

When talking to your client directly : yeah that tweaking will be done, but can u talk my boss into promoting me , I will give u additional services for the next 1 month and won't charge it"

My understanding is that you usually do that during interviews and performance reviews.

But just talk to your boss about it if you can't wait for that. It's an awkward​ topic but it's their job to give raises. Remember that if you're a good developer, you will have grown since your last raise, you will have developed your skills and you'll therefore be worth more money.

Find a better paying job.

I'll be interested to see what others answer as well. I tend to come off rather pushy & bring up wanting more money every chance I get. I'm not sure it's a very effective strategy overall.

Has anyone taken any of the formal classes or workshops about techniques for asking for a raise or finding a better-paying job? I've often wondered if they are worth the money (most are rather pricey) or are just a hand-wavy, double-talking waste of time.