I would go for a trial with a professional (I'm one 
) and then even if you decide not to use her on the day you'll get loads of good tips. Also the Bobbi Brown counters are brilliant and their MUAs will do a wedding day trial for free-they'll want you to buy products but you don't have to of course.
For what it's worth my top tips would be...
Get your skin in as perfect condition as possible in the months before the wedding-that way you can wear less make up. If you have bad skin try the Clarisonic, and stick to a routine of products designed for your skin type, don't chop and change around too much. Personally I love the Liz Earle Superskin range (I have dry skin).
If you're going to do your own make up have several trials while wearing white-if you don't have a white t shirt hold a pillowcase around your neck! (Assuming your dress is white that is.)
Always do your make up in natural light so you can see any errors more easily and fix them-e.g. Foundation tide line, though hopefully you'll have the perfect foundation so that won't be a problem.
On the day: cleanse, tone, moisturise. Use eye primer (I love MACs paint pots for this but Urban Decay do a good one too), then do your eye make up-eyeshadows, well blended, eye liner, eyelashes, eyebrows. Get rid of any powder fall out on your cheeks. THEN put primer on your face. (Smashbox do brilliant ones.) Use a foundation that perfectly matches you-get matched at the BB counter or another good brand. Don't forget your neck, ear lobes etc if you have any discolouration or tend to flush. Use two blushers-one very natural on your cheekbones and one brighter on the apples of your cheeks. You can also contour under your cheekbones (from the very outside of your face to about half way in your cheek), under jaw line, on temples, on outside of nose, and hilight your nose, inner corner of eyes and tops of cheekbones, but go easy on these unless you're used to doing it-practise lots before hand. Don't pick anything too shiny or it'll look odd in pictures. Conceal under your eyes and then top off with a powder to keep everything locked in place-I like the MAC Mineralise range as it's matte but gives a glow without being at all shiny or shimmery. Very beautiful.
Avoid any products with SPF as you can get flashback in photographs. Avoid Touche Éclat for instance!
A gentle application of white or nude eyeliner on your waterline will make your eyes look brighter.
You do need to wear slightly more make up than normal in order to look normal in photographs as it's easy to look washed out otherwise, especially wearing white, but don't be tempted to 'give yourself a bit of colour' with a too dark foundation or loads of bronzer.
Hope that helps!