Question: I am from Madagascar. We are in what is called a "povery trap".
Building a business is very difficult because the population is agglomerating in the capital and the competition is very high. Moreover, there is a lack of public infrastructure that freezes the economy.

What do you suggest me to do as a citizen without any governmental control to have a good impact in the economy?

Answer: 
I appreciate your question because there is an assumed level of individual responsibility. 

Before I offer my answer, I want to make a recommendation. There is a fantastic book that addresses this question in great detail. It's called, "The Poverty of Nations" by Barry Asmus and Wayne Grudem. If you can get a hold of a copy (it's even available in digital forms), please do. They outline a path that a country a can take to move from poverty to prosperity, and make a very persuasive case. 

The simplest answer to your question is, a citizen can contribute to moving his country out of poverty and into prosperity by producing more goods and services. The more wide-spread this type of change is in the country, the greater you will see the move away from poverty and into prosperity. This will lead to people having a greater sense of earned success in their lives. To borrow a quote from Arthur C. Brooks, "Earned success means the ability to create value honestly— not by winning the lottery, not by inheriting a fortune, not by picking up a welfare check. It doesn’t even mean making money itself. Earned success is the creation of value in our lives or in the lives of others."

Now, telling someone that they need to produce more goods and services and have a sense of earned success is easier said than done. Several things can either help or hinder this. If the people are in a country with a lousy economic system, it will dramatically reduce their production of goods and services. Jut a few of these poor economic systems include Hunting and gathering, Subsistence farming, Slavery, Tribal ownership, Socialism and communism. When these types of systems are in play, it will prevent people from getting out of the poverty trap. The more free a people can be, and the more protected from abuse, the more opportunity they will have to succeed. 

In short, a free market will give people the chance and the motivation to produce more goods and services. The right kind of government, which is one where the leaders know and believe that they exist for the good and well-being of the people as a whole, and not just themselves or their family and friends, is one that is going to produce a safe environment for the people.
The best kinds of economic stimulus come with making people better at making businesses locally and internationally.

1/Making skilled tradesmen, new trades, apprenticeship schems, education
2/Making communication with distant rich markets
3/Building organized advanced civil services (town halls, post boxes, churches, police houses) in buildings that encourage fair play and national cooperation.

For the first issue, That is probably where you can intervene...
Education ranges from... giving children dinosaurs and science things to see with their eyes and lego bricks and maths books and soduko... To teaching young and old people trades like: Online Salesman, Treck Guide, Jewelry Fabricator, Honey Farmer, Agricultor... Using modern technologies and latest advances from other countries, for example, you supply some young men with bee-hive construction guide and keeping guide information. 
Mostly you have to find knowledge to do things better from international information sources of researchers of every trade, which means that you have to be able to PRINT information and distribute it... Give people interesting papers to read with plans, techniques, products, on very cheap newspaper. A truck load of paper and a printer is good for printing guides about business development, you can apply abroad for a truck load of paper and a printer. 

2/the second is also a trade, it's like pairing cities up, so that a city in madagascar sais what resources it his and what knowledge it has, and a city in denmark sais what knowledge and resources it has, and they exchange communicationto make direct business expansions based on common interests, like vanilla or something to all the local shops, or local crystals. 

3/it requires investment, but every country should have a prestigious nice architecture for post boxes and town halls and government buildings and police which help for nationality, civility, pride to avoid corruption, and that requires architecture adn funding.