best option would be to strip it down and rebuild with new gaskets etc if you have the money, otherwise dont just try strating it as the pistons may be stuck/siezed in, get a spanner or wrench and socket and try to turn the bottom crank pulley by hand, if it turns the engine then check your oil levels are ok, old oil should be fine enough just to test if itll start for a few seconds, but an oil change after would be a definite, managed to start my sierra after 7 years of no use, shouldnt need new spark plugs just to test if itll start unless they are actually nackered, dont go wasting loads of money on new plugs/leads before you have even tested if the engine will turn by hand, then if itll try to start but with no spark then buy new plugs/possible leads, if it wont turn by hand then you will probably need to take the engine apart and free the pistons and hope the bores dont need looking into, there was some stuff on ebay not that long ago that you could put down the spark plug holes to free pistons if it wont turn by hand, good luck with it hope this helps