This Infographic which is presented by Uspeak & Bluecaribu provides basics to promote mobile apps in two Stages.
Stage 1: Before Launch of the App
Choose a Good name which is Unique and memorable. Choose the right category. Create an amazing icon. Spy on your competitors.
Stage 2: After Launch of the App
Sign up for analtytics apps. Get featured on review sites.Reach out to media.Encourage users to rate app, share it on social media. If you see some traction invest in paid promotion.