How do I get back to a thread I'm following, without searching with much trial and error?

If you've posted in a thread, I believe the default option is that you're subscribed. Just click the User CP link top left, just below the banner. If your subscribed threads have any new posts, they will be shown right there. If you want to get back to older ones, there's a menu bar on the right of the User CP that'll have a link to your Subscribed Threads. Click that.

It says "view all subscribed threads".

I must admit that I tend to go to the top (overview) level and work my way through the different sections. That way you see lots of new threads that may be of interest....

The order of things in the sections change all the time as each new posting brings things to the top of each list.

It also helps to ensure that you see all the stickies which are always worth reading.

thank you! :-)