Greetings from Little England !
What Rick states I fully agree with........but if you want to try starting it regadless, then try the following.
Assuming the bike does not need brakes or running gear servicing, then I would advise the following procedures BEFORE trying to start it.
Drain & replace all fluids including engine & diff oil.
Replace oil filter & clean plugs (no need to replace unless really bad).
Check / clean air filter.
Fully charge or replace battery with a good one.
REMOVE CARBS and completely strip, clean & refit.
If the bike has not been run for a long time, then the fuel that was left in the carbs 3 float bowls will have turned into a horrible varnish & will be lining the insides. If you just flush the carbs through & try to start it, you will suck up all kinds of rubbish & bits of dried fuel into the carbs themselves & make the whole thing a lot more complicated.
Finally I would advise removing all 6 plugs & pour a little engine oil into each cylinder & leave for an hour or so to soak the rings & line the bores with lubricant. Next, turn engine over 20 or so times at end of the crank with a spanner very slowly just to get things moving before replacing the plugs. If you feel any resistance or stoppage when turning engine with the spanner THEN STOP IMMEDIATELY & DO NOT FORCE IT.
It is quite common for the rings to stick to the bores after prolonged periods of no use, and can snap or damage the bores if not lubricated.
If you want to be 100% safe, then remove cam cover & pour engine oil over everything inside & around the cams & 12 valves as they will be very dry, which is not good for starting.
Please let us know how you get on !
Pete F