Richard, those two certainly rate near the top of my list. Time management seems a perennial challenge in any area. Broadening the idea of topic selection, I’d add keeping a feel for the hearers and their needs, an ever-present challenge, and maintaining a balance of biblical topics and a proper spread of work across the books of the Bible. On the latter, with my NT reading schedule determining my sermon texts, I’ll surely do a better job of representing the books of the NT. This year will see a dearth of OT sermons, however. The best we’ll do there is reflect OT background, quotes and truths inherent in the NT texts.
Also near the top of my list would be paring down the sermon to get to the essence of the topic.