For a student, what is the optimal usage of a solution manual? During coursework if a solution manual is available for the textbook, it is always a huge bonus for the student. While the student is exposed to a variety of relevant applications and tricks in the problems, the solution manual ensures the student's hard work spent trying out the problems does not go waste. The solution manual's availability is akin to the presence of a "Cheat" button in crossword applets - the earlier you press the less you try, but still the presence of the button is useful as such. 

What are some useful tips for a student who wants to utilise the solution manual optimally?
Never use the solution manual before trying everything else; talk to friends, visit the professor, go to class and listen (!), check the internet. Once you use the solution manual for a problem, the potential gain from that problem is significantly and irrecoverably reduced.
Use the solution manual to check your work. (Duh.)
For problems you aren't planning on solving, you can use the solutions manual to create flashcards and other learning aides (if the course material is anemable to such a construct).
If you have a friend/roommate/spouse/trained monkey who can compare your answers to the manual for you, such that you don't actually read through the manual, that may be useful for certain topics.
You can make some good money selling it when the semester is over :)