You must be able to carry out some of your own "personalised" calculations.
The topic must involve something wider than doing calculations.
Consider what higher level analysis you will be able to carry out on your initial calculations.
You must be able to find at least 3 books / academic journal articles on related mathematical work.
If you are learning about a brand new area of Mathematics, you will often find course notes from top universities useful. If you are able to, it might be useful to buy a book aimed at undergraduate students which explains the topic fully. When you are trying to get your head around new mathematical concepts and terminology, wikipedia is actually very useful. Get stuck into your calculations as quickly as you can. Keep checking, and take calculations to your supervisor early on for checking since mistakes on this level can really impact the quality of your EE. Once you have completed your basic calculations, which is a bit like gathering data, think about how best to analyse these. The more levels of analysis the richer your critical thinking.
Ensure that your introduction explains what you have chosen to investigate, why this is interesting and worthy of investigation, what calculations you will be carrying out, and an overview of what your results show. By the end of your introduction, the reader should know what the answer to your research question will be.
Introduce areas of Mathematics you use which are not part of the IB syllabus, but try to be brief or your EE will become too descriptive. Define terms and variables precisely. Give an overview of your calculations, there is no need to write-up repetitive calculations, showing a method once is enough. Sometimes very lengthy calculations should be moved to an appendix. Make sure that all mathematical working, expressions and variables are presented using equation editor. Ensure that you leave enough words for the analysis of your results.