Frank Lloyd Wright believed the hearth should literally be the centre of the home, so it's a good idea to make sure yours is ready to be the centre of attention.
This is a great off-season project because, hopefully, our fireplaces will be on hiatus very soon. Looking at the insert or actual fireplace itself first, a common issue is outdated brass trim. I've pleasantly surprised a number of my clients by pointing out that the trim is often simply attached with magnets, or easily unscrewed and removed to reveal black metal underneath. That easy, free update is great, but if your brass (or other dated or damaged trim) isn't easily just removed, mask off the areas you want to protect, and give it a few coats of black barbecue paint. It's heatproof and is great for this application.
The immediate surround of your insert will probably need to be heatproof. Check the manual that came with your insert to determine the clearance needed. There are zero clearance units, but many gas, and all "real" fireplaces need some allowance of non-combustible material around the opening. Selecting a tile or stone for that area is where you really get to have some fun, anyway.
Lastly, the mantle can often be updated with some paint. Look at the proportions and see if it needs some beefing up first. In the example shown, a bit of extra moulding was added to the mantle to better balance the top with the sides. A dramatic improvement can be achived through DIY or with just a bit of professional help and your fireplace can be the beautiful focal point that it should be.
Need help putting together finishes and design ideas for updates to your home? I'd love to be of assistance.