Where can you find the information for your indicators? You can make use of:
In some cases it may be interesting to have various sources of information that you can compare to each other (triangulation). Or you may need to combine different sources of information to get a complete picture.
Another question is how you will practically gather the information: using registration forms or questionnaires; registering it in a database or a spreadsheet; doing surveys… You must also decide on how regularly you will gather the information. And last but not least whose responsibility it is to gather what information.