I think series one had two specific points that the spinoff novels fit in to timeline-wise?
The Nine, Rose and Jack novels had to fit between The Doctor Dances and Boom Town thanks to being omitted from Rose's flashback to the events between Boom Town and Bad Wolf. Boom Town also features an onscreen reference to one of the Nine and Rose books, which I always thought was a nice touch, even though The Monsters Inside was crap.
I think the earlier Nine and Rose books slotted between The Long Game and Father's Day, but I couldn't swear to that off the top of my head. There's a short story compilation which uses the events of Last of The Time Lords as a framing narrative
There's an Eleven, Amy and Rory book that ends with them heading for Rio, which sets it pretty firmly directly ahead of The Hungry Earth/Cold Blood.
On a slight tangent, it's interesting to read Made In Steel, the Quick Reads novella that they brought out back in 2007. It was the first piece of media written featuring Martha Jones, and it was released a month before she debuted on TV, but Terrance Dicks was working from early scripts and character outlines, so a lot of the details of Martha's life were slightly out from what was on screen. That's another one set between two specific episodes, actually; has to be between The Lazarus Experiment and 42.