Once you have your idea one of the first things to do is follow the practice of industrial researchers and conduct a preliminary literature search to determine that your invention has not already been described. Quite simply, maybe someone else has already had the same idea and received a patent. Further investigation is not a wise investment of time without knowing your idea is novel.
The next thing to do is test practicality: do you have something that the public is willing to pay for. Under the conditions of the patent law, your discovery must be "useful." This means that your discovery must have a purpose and your invention must work. The process of making sure that your invention will work to perform its useful purpose is called "reduction to practice."
To physically reduce your invention to practice, you must make and test your discovery under actual conditions of use.
Some examples:

• A new insecticide might be reduced to practice when it has been produced and used with success for its intended purpose of controlling a specific pest.
  
  
• A mechanical robot might be reduced to practice when it has been built and used successfully to carry out its intended function in an auto assembly line.

It is not always necessary to physically reduce your invention to practice. You may use lab tests to demonstrate usefulness. Filing a patent application also is a type of reduction to practice.