Used to be /r/programming... not anymore though. Just go to techcrunch and wired.com, that way you'll see everything that makes it to proggit - but only once, instead of every day for a week. The more specific the better, provided there's a lot of subscribers and there's regular new developments in the topic of interest. So /r/doctorwho sucks pretty hard when the show isn't in season. There's a lot of crocheted figurines, etc, it's painful.

/r/bicycling, /r/motorcycles and /r/autos are all great, but /r/justrolledintotheshop is brilliant because of how specific it is and how there's always new content - ie. picutres of idiotic things customers bring to their mechanics. /r/scooters is not great because the community is too small.

The subreddit for my phone is of interest. Programming languages that I'm trying to learn - Python, Scala. Skills I'm interested in - welding, CNC machinery.

Well, that's a good start if you're into things on wheels and programming, anyway.

http://www.reddit.com//r/AskHistorians/ is easily my favorite subreddit. The quality of the lengthy submissions and the fanatically rigorous moderation is amazing.

http://www.reddit.com//r/DepthHub/ is a great highlighter for introductions to quality subreddits. Its how I found /r/AskHistorians/

http://www.reddit.com//r/BestOf/ is good too.

Other than that it depends on your particular interests.

There is an outstanding problem that subreddits I would love exist but are hard to find. However that does also protect them and their mods from the slavering hordes of captioned gif posts.

It depends on what you're interested in.

I'd start by, say looking at a set of current tech sites, seeing what current articles appeal to you most, and searching for those at Reddit. Look for the subs they turn up in and check out the conversation.

I'm actually mostly following subs that don't have to do with IT issues (programming, systems admin/DevOps, or networking) as I'm finding my interests lie elsewhere. One rule of Reddit is that if you can imagine it, there's a subreddit for it.

One G+ feature I'd liked was the fact that my posts there formed their own channel, a feature somewhat lacking on Reddit. I've created my own user subreddit as a place I can post and curate my own links or discussions. Not sure if I'll keep it but it's an interesting idea.