As most of the general-purpose programming languages, there is not a single methodology for using SARL.
Usually, me and my teams are using a standard agile methodology with several steps that are inspired from our complex-system design methodology
ASPECS, when we do not require to use a so complex methodology.
When implementing with SARL, read carefully the document of each function. Indeed, several of them may have a strong impact on the run-time because they are run in parallel to the rest of the application.
Keep in your mind that every "on" block is run in parallel to the other.
From that, you will have to be carefull about the distributed system design of your multiagent system, and its implementation with really parallel features.
Think event-based implementation.
If you have any question, do not hesitate to come back on this forum.
Stephane.