Construct a wind-star at the same time as writing up your PLOG.
This is the method I was taught and find very useful. The wind-star should contain the
drift for that particular heading along with the expected
groundspeed.
1. When told to divert draw a line from your start point to the destination. Measure that distance with your ruler (I use a CPM 1 in flight).
2. Estimate the track to fly.
3. Adjust that track for the drift indicated on your wind-star to get your heading.
4. Consult the wind-star again for the groundspeed. With that in mind use a CPM 1 to find the time it will take to fly to the point of diversion - with that you can work out your eta.
Monitor your progress as usual and update ETA and headings if they appear to be different in reality.
Personally I really enjoy practising diversions, you have to be on your toes to stay ahead of the situation. If you are finding them hard then ask an instructor to go through them with you. Good luck.