The most effective type of persuasive communication would primarily be face to face.
This will establish a personal connection, and you can also incorporate other persuasive devices such as eye contact and body language while speaking. Something you wouldn't be ale to to do if you were using email or a phone call for example.
Persuading groups in an organization
To persuade someone, you will often need to convey a message that will somehow change or reinforce their response. In this case trainers, employees, programmers and managers.
Therefore you will need to prove knowledgeable and trustworthy in the area in which you wish to persuade.
It may also be useful for you to incorporate informal persuasive communication. This is done by asking the right questions and discussing different options, as this way you can bring someone round to your point of view.
For example by asking people questions you can identify their needs and doubts about the ideas you are putting forward, then demonstrate how you can accommodate these needs.
When communicating verbally do not doubt how effective non-verbal communication can be! As this can have the power to influence sometimes as much as verbal.
For example if you cross your arms this could be taken as you being hostile which is not how you want to come across. If you fidget or pace then this can be a sign of weakness or uncertainty.
It is important that you maintain eye contact, and stand up straight as this will show confidence, and have your arms relaxed or use them to gesture.