Gas milage is your best indicator of when it's time to open the tool box. It can be a number of things. Did you say "Recently Purchased"? Congrats!. A full tune up would rule out a lot of the easy things, and, considering the year (97) the vac line is suspect and easy to rule out. Let's assume the previous owner performed zero maintenance for the last 3 years.
Change the oil & filter, set the valve lash, change the spark plug, air filter, fill the battery, decomp solinoid check , fill the tires to the correct pressure(check for rot) and check the brake pad thickness. These are things that you will do at least once a season anyway.
Become one with the motorcycle, sleep with the Clymers manual and make suzukisavage.com your home page