Most of the clients are prompt and pay the money on completion of the project. While some companies agree to pay the amount as soon as project delivery, it never happens as expected.

The reasons they give is that they are testing, or that they are out of town. They'll say "Please bear with the delay we are expecting some income from other sources."

So in such cases, having advance payment prior to project development is better.

How do I handle the contract situation in such cases? How do I make a contract prior to project development?