I am really bad at coming up with time estimates for coding projects, and I'm getting asked to do that more frequently lately. Can you please share some tips or techniques you use for this?

My rules of thumb are:

1. Any individual estimate over three hours is a guess that can be wildly incorrect. Split or simplify tasks until they're all under three hours.
2. Try and keep all of your tasks about the same size. It makes moving tasks around and re-prioritising so much easier.
3. Look at how many tasks you did last week. Assume that's how many you'll do this week. Adjust milestones appropriately. (aka Yesterday's Weather)