You really need to work backwards from the value of the customer. If you have something that directly monetises then you can calculate value of a register user

You really need to work backwards from the value of the customer. If you have something that directly monetises then you can calculate value of a register user and of a visitor. Back out your marketing budget from there. However I am assuming you have a consumer app where it is very hard to calculate the value of a visitor/user. In that case you are looking at viral, social media, SEO and paid ads. Viral works if your product is intrinsically viral product (send to friend doesn't count). Social media works if have rich content (how to's, great photos, recent news). SEO is what you do if you can't do the first two (I know of one of the world's biggest travel social networks who never paid a penny on SEO). The problem with SEO is it takes a lot of time to build up traffic. That brings you to paid advertising. I think paid advertising is great for getting everything kick started but the business model for paid ads doesn't stack up for free consumer apps. Hope that helps.