Repeated-measures ANCOVA - Handle assumptions and missing data (SPSS)

Hi all,

I am performing a repeated-measures ANCOVA in SPSS with following characteristics:
  • Dependent variable: weight loss (with three points in time)
  • Independent variable: conscientiousness
  • Covariates: gender, age, depression
I can't find a good online guide that will take me step by step through this analysis. I particularly have questions about this:
  1. Which assumptions do I need to check and how to handle violations?
  2. In the measurement of the dependent variable from the second to the last point in time, I am missing 64 data points. How can I best handle this missing data?
I hope you guys can help me out. A reference to a good online source or video tutorial would also be extremely helpfull!

Thank you for your answer. I found several tutorials, but none seem, in my opinion, to be thorough and step-by-step. I was hoping to lean a little on the experience here and find the best one immediately ;). I have been missing it in Andy Fields book, which I like. I will share of course if I have found the perfect one.

If anyone has a suggestion, still open for it! Thanks!