Don't do it yourself. You wouldn't attempt to fix your car's air conditioning so why try to design something yourself? In the long run, you'll save time and money investing in the services of a professional graphic designer. Not only will they do it in half the time but will also create the artwork in the correct format for which it is intended.
Involve your graphic designer at the beginning of projects, not half way through. Your designer can contribute new ideas from a different perspective and will also be aware of new and emerging design trends that can put you ahead of the rest.