Reddit mentions of Colour Atlas of Rocks and Minerals in Thin Section

If your working with thin sections i'd suggest Gribble and Halls book, Not sure what level of detail your looking for but MacKenzie's rocks and minerals in thin section good to get the basics of optical mineralogy from.

If you've never done Petrology before aquiring a good lab guide will be very useful, the one my university recommended us to get was:
http://www.amazon.co.uk/Rocks-Minerals-Thin-Section-Colour/dp/1874545170/ref=sr_1_1?s=books&ie=UTF8&qid=1451826653&sr=1-1
This helped in my first semester of Petrology a great deal. To accompany this I also, as Of-Quartz said, took pictures using my phone of the thin section down the microscope. I then created a study guide to accompany these pcitures, Example for Olivine:
http://imgur.com/7KBPGE4
The exam itself was based more around the theory side of petrology, End member diagrams such as Kynaite, Silimanite and Andalusite, along with general questions about Bowen's recation series and other figures that help explain why the thin section you're looking at, looks like that.

As for Sedimentology and strat you'll be looking at photos of outcrops and sedimentary successions alot. Sedimentary logs, Bouma sequences and identifying features such as Load casts, flame structures and dessictaion cracks to name a few.

Just make sure you understand the fundamentals and everything else should come to you easily.

3rd Year geology student (UK), Taken Sed/Petro classes every semester.

http://www.amazon.com/Colour-Atlas-Rocks-Minerals-Section/dp/1874545170/ref=sr_1_1?ie=UTF8&qid=1462489109&sr=8-1&keywords=An+Atlas+of+Minerals+in+Thin+Section

Get this book! It's awesome for minerals.

I too have trouble with this, but I'm making slow progress purely through practice. I find this book quite helpful: Rocks and Minerals in Thin Section. Other good resources I've found online is Alex Herriot's collection and this collection of thin section from the Bushveld Complex

https://www.amazon.co.uk/Rocks-Minerals-Thin-Section-Colour/dp/1874545170

This book did wonders for me during my degree, give it a look, worth getting a second hand copy on the cheap.