I'd recommend using ARIA for Live updates, at least that's what I think they're called. For example; let's say you have 100 characters left in a text box, and you're writing and writing and then,, oh no! you've gone over the limit. With ARIA as far as I understand it, screen reader users can get an alert telling them that this has happened. It's alot easier than having to go out of forms mode or focus mode and then checking the amount of characters remaining.

I'm blind and my job is to do accessibility testing for Temple University. Check out the Web Aim wave accessibility tool.
http://wave.webaim.org/
I use the firebox extension every day, and I think it's a good tool to have in your arsenal. Wave will flag a lot of accessibility issues and concerns and explain why they matter. FYI, tools like Wave are never as good as simply testing web pages with assistive technology. It's great that you’re testing with NVDA.

NVDA is a good option. If you have an iPhone, you can try turning on Voiceover and testing your software with that. I recommend turning on the "screen curtain" feature that blacks out your screen so you get a better sense of how it would actually be to use your site or product.

There are many things frequently done wrong on the web, but the two most common are no or poor alt text on buttons and images and a lack of semantics.

The alt text issue is actually more common and annoying for buttons, search boxes, etc., than it is for images, since often it's not really important to know what a particular image is, but it's really annoying to hear the word "button" and not know what it does. Most screen readers have a labeling feature so you can experiment and name things yourself, but obviously that's annoying to have to do.

Semantics means using elements for what they mean, rather than what they look like. While for sighted people a list formatted with CSS might look like a table, a screen reader user might not be able to understand that it's a table or interact with it properly unless it actually uses table tags. Similarly, sighted designers often use heading tags indiscriminately because, say, they think the <h3> tag looks nicer and let's just go with that. But if you're laying out a page structure, it's really annoying to be a screen reader user and to have the heading tags have no semantic meaning. Similarly, it's better to use <nav> than to use a styled list (though I'm guilty of that one myself).

Good on you for taking it upon yourself to learn about this.