Start by draining all petrol and replacing, remove carb's drop float bowls and lid's, clean, remove/clean all jets (make a note of whay's where and keep for future reference (ie if it all goes tits up (not speaking from experience mind....)))!
Measure float height.
I would remove the stuffers (bits the carbs bolt to) have a peek at the crank for debris or corrosion and squirt a bit of oil onto the moving parts for first start up.
New plugs, check power valve ajdustment and make sure they're free best to remove and lube the cables, probably the valves too.
Have a good look into the bores for damage - plug holes/exhaust ports.
Squirt a bit or 2stroke into the bores and kick over a few times.
Safest to drain oil tank and put fresh Fully synthetic (only) 2 stroke oil in .
Make sure the bike has a good battery on.
Start up outside or you're sure to choke as your steed creates it's own little micro-climate!!!
Enjoy.
Regard's, Phil