This depends on your age. First of all, safety is the obsolute first priority (pole vault, high jump, throwing events, hurdles). If you are competitive, try not to let previous events bother your current event. Don't set the bar too high so you won't be disappointed. Aim for 2000 points. After all, this is decathlon "2000".

The only way to compare is by raw converted points. There's way too many variables and uncertainties if you want to say give today's training, nutrition, and equipment. You could also look at today's pressure, today's peer influence, or even air quality.