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!