go HERE and get the Vespa manual near the bottom of the page.. Become very familiar with the bike..
Read Fred's Guide at the top of that page..
no-start after a long (or short) period of storage is undoubtedly due to old gasoline decomposing and sried resins and junk are clogging up the fuel system.. The entire system, from tank cp to carburetor should be cleaned thoroughly, first thing..
If it still doesn't start, come back here describe the trouble and ask.. and use the "Search" link above .. there's tons of specific information, questions and answers in the forum's archives.
Try this.. buy a can of Starter Fluid at the autoparts store.. Squirt a bit into the carb air-intake or into the spark plug hole.. replace the plug.
If the bike then starts, fuel supply is restricted but the bike's ignition is ok.. and the whole engine is probably in good shape too..