As often stated (probably?), I think website design can be broken down – writing copy, writing code, doing graphics/layout and designing experience (UX; a combination of all). You probably don’t need any more practice with the first but the other three have many avenues. UX is worth your while and severely needed in the nonprofit world, but you’ll have to do some translation for many of those folk. Coders don’t exist there. Developers are a rare pink unicorn in one of those scenes from planet earth with millions of birds. Coders often aren’t socialized to do world-saving work, and they get paid gobs in other fields. Graphic design is handy for all of the things (print, web, identity, making, life) but also kinda hard to learn without specific projects. Luckily you have some of the foundational skills, like the ability to notice details or general concepts like negative space.

SO substantive resources:

• For coding – you could learn HTML/CSS but I think it might be more helpful to learn an introductory language like PHP (and MySQL for databases to go with it – this is what WordPress is based on). There are many free online resources, start with W3C Schools and go to something more serious from there. More hardcore (application-specific) people may tell you to go for Python or something off of this list -> http://www.hongkiat.com/blog/sites-to-learn-coding-online
• Graphic design – I have a book that’s trapped in storage in Glen Ellyn right now that has a hundred great design challenge prompts. Tasks like make a mail-order army of robots. I’ve done a few and like it, but I think learning how to operate fancy-pants programs is as much of a challenge as figuring out how to make things look good. One route is to learn to make great looking designs using simple tools, like Powerpoint 2010 or 2013 (better the newer you go) or another is to just start following scripted tutorials for Photoshop or Illustrator. Try learning the pen tool to make paper cutting designs, you can make money better than Kay Wahlgren and help dad retire. I can probably get you any Adobe program you like, or try Inkscape or Gimp (the true we-have-no-money route).
• User Experience – See if you can get into this class -> https://www.coursera.org/course/hci. Don’t bother with the assignments, just watch them. It’ll teach you concepts behind usability and user testing methods. Or you could try reading The Ten Faces of Innovation by Tom Kelley. My professor uses this to teach composite design in LIS (an interdisciplinary field that likes people!).

I think ‘social media’ skills are a little overrated. It’s worth learning the capabilities and social norms for each network or medium but I encourage people to pick just a couple and commit investment to those. Generally my impression is that what lies beneath them are good writing for the affordances of each and a sense for audience – things I suspect you already have 🙂 But this might also be that I just feel annoyed by continuously hovering over a monitor watching the endless flow of information stream by, with meager attempts to redirect it amongst the flurry of hyperactive internet squirrels. I’d rather be more selective and intentional with my attention, something I think I’d even call a digital literacy. Yes, thank you Howard Rheingold, but I still think meditation is silly.

I’m not sure what general tech skills might be. You can move a mouse and type pretty darned well, and glean information from different screen formats rapidly in a non-linear fashion. Check.

Anyway I think you nailed it. Pick a project. Shattons of nonprofits need help. I just talked to the Urbana Independent Media Center Python Users Group the other day. The Fab Lab has plenty of things they could work on for us – a better sign in system, automated inventory, an interactive project board or hacking the CCK in our broke-ass Drupal install to be friendly for retirees. Or many groups have crappy looking websites or need better flyers or logos or good looking report designs. Perhaps better than this – you could learn video production and help a group produce their image on YouTube by telling a story about the impacts they make (CI Club example – http://youtu.be/_pBjjW2E2Mg), a lot don’t have time or knowledge to do this kind of thing. Or many service users whom they have never tested and may have vastly different understandings of computer interfaces than they do. I learned my friend’s mother doesn’t really know how to save and upload photos of her daughter to Facebook to share so she just tags herself in them instead. This is in part an interface design issue – I’m sure the system could be recreated to facilitate this behavior and perception of use.