This is my first year post-seminary, and I realise that one learns a lot of things in that time. Here are a few things I've picked up that might help somebody.
1) Be prepared to do a lot of theology!
If you're involved in any sort of teaching ministry, one of the things that becomes readily apparent is that you develop the need to figure out all sorts of things that you may have thought about, but haven't thoroughly explored or come to a position on. For myself, this is probably reinforced by having an open question time after sermons, preaching every week, and tackling any topic that comes to me. What it means though, is that I regularly have a single week in which I'm preparing to understand, comprehend, reach positions on, and teach large slabs of doctrinal and biblical material.
2) Start keeping some kind of record of things you've taught on/addressed
Personally, I do my best not to repeat the same ground - preach on the same text, run the same bible study, etc.. There's a lot of Bible, and the more of it I get to, the better for everyone really. Nevertheless, undoubtedly there will be times when somebody or something wants me to cover X, Y, Z. For that eventuality, I now keep a simple spreadsheet in which I record what texts, topics, etc., I've done some work on, and a few notes about what materials I've kept (recordings of sermons, notes, etc..), and what materials I found helpful (commentaries, etc..), so that if/when I do come back to that, I can look up those things and go from there.
3) Develop a system for keeping notes, articles, etc..
I don't mean filing in general. What I mean is this - say you've ended up with 4 years of seminary notes in one big pile. Perhaps you've also got 50 articles on Matthew kicking around. Shoving these into archives doesn't really help you. Keeping some kind of index does. For me, I've basically decided to assign a four-letter code for topic (eg. MATT), with a 4-number sequence (eg. 0001), keep them in order, and maintain an index file. So, when I need to read some things on Matthew, I'll pull up my index, find what I'm after, and go find the article. It's like a mini-library of serial articles.
4) Make sermons available for free.
If you're going to preach sermons anyway, in your church for instance, then I don't think you have any good motive for selling sermons. Don't you want people to hear the word of God preached? If you actually believe in what you are doing and saying, then get it out there. My sermons may not get huge amounts of downloads, but if a few extra people listen to them and it does some good, then nothing lost and much gained!
5) Get a decent book budget
I only speak about this from negative experience. Due to the peculiarity of my position, I don't have anything like a ministry expense account, and so any purchasing of books comes out of my take-home salary. Which, I suspect, makes little difference overall (since books should be tax deductible), but it does make a psychological impact nevertheless. Buying commentaries, etc., is not cheap, and so far this year I've bought zero books related to my preaching program. I am blessed with still having access to the resources of a great seminary library, but I do think that given point-1 above, this is the time you want a young minister to be buying up some solid reference books, getting into the scriptures and studying them well, and I'd much rather be buying some commentaries than borrowing them and maxing out my library card.