If you want to submit a patch for inclusion – from solving a typo you discovered, up to adding support for a new feature – you should submit it as a bug report, using the process in Bug Reports. There are some things that you can do to increase the chances for it to be included in the official package.
Unless your patch is very small (say, under 10 lines) we require that you assign the copyright of your work to the Free Software Foundation. This is to protect the freedom of the project. If you have not already signed papers, we will send you the necessary information when you submit your contribution.
For contributions that doesn’t consist of actual programming code, the only guidelines are common sense. For code contributions, a number of style guides will help you:
If you normally code using another coding standard, there is no problem, but you should run the ‘indent-gnutls’ script found in the ‘devel’ directory to reformat the code before submitting your work.