Assembly is a great language.

A good book is Introduction to RISC Assembly Language Programming by Waldron 0201398281

RISC= Reduced Instruction Set Computer. It is a good little book to start with.

Also you could get Computer Organization & Design by Patterson Hennessy 1558604286

If you are using an intel chip you could get The Intel Microprocessors by Brey 0139954082.
But you could get into trouble.

You should start with the Waldron book, and use a simulator. You can ftp a simulator from ftp://ftp.cs.wisc.edu/pub/spim that goes with the book. Or better still write your own simulator. They are not too hard to write and it will give you a better understanding of assembly