I used to hate this. I still hate it, but I used to hate it, too.

More seriously, something that has helped from my managers is getting a "product requirements doc" or PRD. Management and customer reps put together a requirements document that says what they need built. Then you can break it down into work units for yourself and estimate the size with milestones and deliverables. It helps a bunch, even if it's extra overhead at the start.