If you apply the decal with wet method, it is foolproof.
Its the same as applying vinyl signs and pretty much guarantees a bubble free finish that is perfectly in place.
Use a garden spray with water and approx 2 drops washing up liquid in it.. give a good shake.
spray the apron and peel the decal. apply decal to wet apron.. it will slide over the suface allowing you to position correctly.
once in position, hold the centre down and from the midle of the decal out push the water out from underneath using a firm cloth etc.. actually driving licences are great fro this if you dont have a vinyl squeedgy.
Then push water out from other side.
Put aside to dry.. can place in sunlight for this.. every now and again running your fingers over the edge to ensure good adhesion here.
Surface MUST be grease free... no fingers!
IF you do get a bubble then prick with a sharp scapel and push air and water out.. you wont see the hole so long as its a prick not a slice.
If the decal has a problem settling into the crevices where the instruction cards sit.. wave a hairdrier over it very lightly.. this will soften the decal and allow you to laminate it into place... you can push it down with your finger... its how we apply to crevices when wrapping a car.
If you do it dry.. you WILL get bubbles/ creases and very likely off centre.
If you know all above already, then i apologise for teaching the sucking of eggs!
Wow, thanks gavin!
i didn't realise all the possiblitys and problems that could happen, i thought it would be easy to just put down the decal evenly, i think i'll do the water and deturgent idea when it happens and hopefully i dont stuff it up and need another one! 
You should'nt have any problems applying the decal following Gavin's tips. Only thing i could possibly add is to make sure you dont get any specks of dust etc on the apron as the decal is being applied. probably not a major issue with this decal as its black, and not clear, had that happen to me once with a Gottlieb apron decal (speck of dust under a CLEAR part) 
lucky for me though it was near an edge and i was able to remove it.
Sorry if i missed it elsewhere in the thread but are you repainting the apron before applying the decal?
no you havn't missed anything! i'm going to spray the Apron with the left over Satin Black that i didn't quite use up for the cabinet...
i'm not going to finish the apron anytime too soon because i havn't started the playfield and if i finish the Apron now it will proberly get damaged before i finsh the machine! i need to do the Playfield stickers and touch ups with dads airbrush on the playfield before i get too caried away with the Apron. I only really decided to look at the apron because i havn't got my cabinet stencils yet... they should be here this week!
