Just thought I'd update, and say I found my first cache today. Stopped off at the Follingsby roundabout on the way to Heworth, and found one there within about 10 minutes. There was another one I wanted to find on the Quayside, but after about 30 minutes I couldn't find it there at all.

It's quite interesting actually. The first was a lot easier than the second, as it's hard to not look suspicious on the Quayside during the day, when you're searching for something