Platforms (or starting a scene)
Platforms are the start of the scene, and are where you establish what your scene is about. The important thing to remember is that you don't have to be interesting or funny as soon as you hit the stage. What you should be focusing on is building the world in which your scene is going to take place. The richer the world you build at the start of the scene, the easier you will find the rest of the scene which follows.
Below are some suggested ways you can start a scene. None are necessarily better than the others - it is important to find an approach which works for you. What they do have in common is that they are about creating a world from which the rest of the scene can then emerge.
Establish the who, what, where (who your scene is about, where it is occurring, and what is happening in it).
Bring one strong thing to stage (a voice, an emotion, an attitude, a physical trait).
Establish the main relationship in the scene (how do you relate to the other characters).
Hero and quest (who is the main character of the scene and what is their quest)
Explore your environment (flesh out the physical world of your character).
One final suggestion is to start your scenes with positivity. Performers have a habit of immediately picking fights in a scene, in the belief that conflict is entertaining. What is often more effective is to start the scene without conflict, so we can get to know the characters and, more importantly, begin to care about them. It also makes any bad things which eventually do happen to them far more effective.