There is no single number (apart from 100%) that can be termed as ideal accuracy. But a more useful parameter to consider is desirable accuracy.
This too will vary for each one of you.
1. It depends on your strengths and weaknesses. You should aim to maximize your accuracy in topics/areas/sections that you are really good at.
2. It depends on the relative difficulty level of the test. So, tough, treacherous terrain is where you slow down and ensure a high accuracy/control, because more speed will just mean more accidents.
3. It could vary a little across sections – English is usually tougher to get a high accuracy in.
Now, just to satisfy your curiosity:
70-80% Accuracy in English (VRC), 75-90% in DILR and 80-90% in QA are excellent levels for accuracy if you are aiming for the Top 5 %ile. But bear in mind that these are just indicative ranges and you could succeed despite not meeting one or more of these, depending upon the difficulty level of the sections and the performance of your competition, and of course the number of attempts you make.