Make sure you do some investigating when selecting a videographer. There is a reason some videographers offer dirt cheap rates; it could be that they have none or very little experience and you get a lot of junior videographers that are not able to capture everything due to a lack of experience.
Its advisable to investigate and get portfolios and find videographers that have great testimonials and have contactable references. You only get married once and you cannot recapture all of your moments so its essential that if you want to have a professional photographer that you have done the right research and also prepared a budget as these services do no always come cheap. Double check and make arrangements to meet up with the videographer, chat and ask as many questions as need be and ensure the videographer knows exactly what it is that you want as in effects way and which parts of the ceremony and venue are important to be captured on screen.