Short trips = Less Fuel efficiency
Long Trips = More Fuel efficiency
Anyway, please check and clean the Plugs & Air filers first.
There are plenty of fuel system cleaners* (3M, Würth) in the market. I am using Würth in every 6 months. Price may be around Rs. 1100/=. Good results. 3M also good.
*Fill up the fuel tank first and insert the Fuel system cleaner in to it. Dosage may be around 50:1 (50Ltrs per one bottle).
If this is not work, better to have a engine tune up.
Read this:
Good Luck.