Ken Rubin is a fantastic teacher. A few of his nuggets from Essential Scrum:
Keep the backlog to a max of 150 tickets. Delete the rest (like the bugs that have been sitting around for years). Or move items, like bugs, to a separate bug tracking system.
For release planning, draw the line for must have features, and another line for nice to have features. Break out features into engineering tasks. Consider using story points for features, where only the relative values are important, and using hours for tasks, where the actual hourly amount is important. Don’t fill a sprint to 100% capacity. Leave a buffer of about 20%. Estimate sprint velocity with a range, 90% confidence with standard deviation, etc.