If you built a software like (web app) but you need to reach to more clients to sell it .. How do you do to market this app successfully and efficiently ?. Thanks a lot ?
First - know who your target market is. Where do they hang out? Hashnode? Hacker News? Instagram? Facebook? Twitter? Elsewhere ?
On Twitter and Facebook - gaining friends and followers is free and relatively easy. Friend people, follow people and get them to follow you. Make relevant posts that engage your customers. Try to stay on topic and don't be annoying - but keep in mind, you can't please everyone.
Second - learn what they like. Do they like contests and to win something? Do they like logo wear? ie: products branded with your logo? Giving away a $20 gift card could be negligible if your service has a $20 monthly fee.
Third - have great customer service. Answer your customers quickly and promptly and to the point. Never give away the farm, but make sure your customers get what they need, when they need it. If you charge for your service and someone wants a refund - so long as it's a valid reason, do it.
Forth - Talk to people. Get to know your customers, what they want, what they need. Everyone that has a product to sell should have an elevator pitch. An elevator pitch is roughly 20-30 second; and an overview of a product, service, project, person, or other thing and is designed to get a conversation started. Your not trying to sell someone with an elevator pitch; your just trying to start a conversation. After the conversation starts, start asking questions. What do you do; What problems do you have with X; what do you need?
If you have marketing money
This all changes. A few Facebook or Twitter advertisements can go a long way. Again, don't be annoying, but learn who your target demographic is and market towards them. Facebook actually has really great marketing tools and collects amazing amounts of demographic information. A little research and work and you stretch a dollar pretty far.
Google Adwords are another great option. This can be more expensive depending on your keywords, but is another option.
If your product targets a local market - look into radio advertisements or newspaper ads. Newspapers aren't dead yet and a lot of people still receive them.
Lastly - you never said what your app does. Tell us - maybe someone here has a need for it! Or, we can at least give you constructive feedback on it.
Samuel Oloruntoba
Java is to JavaScript what Car is to Carpet.
Adding to @mgiambanco said, I would suggest using Envato services, stuff like ThemeForest and CodeCanyon. Envato has a large market and people can easily sell their web apps.