You've got the hardware and the software but what does it all mean ?
This book takes you through the basics of analysing your logged data - even a few simple measurements can yield a surprising amount of information which can result in increase performance on track. It includes lots of real world examples using real data also you won't find complex math here.
The book also makes a brief exploration into the kit professional teams are using for data logging and analysing.
Its also the only book I have found on the subject, which kinda makes me think that the analysis of such data is an art and involves hard won knowledge.