I think rosemary is supposed to be trimmed at this time of year, but I'm not sure how to do it. The tips on mine are quite brown so might try cutting it back. Any tips?
You can cut as far back as you want..but you need to have some green growth left bellow the cut for it to produce new growth.
Rosemary is not too happy with severe pruning and particularly more its done nearer to the old wood. I treat it bit like lavender..mine gets severe haircut for all those nice 'fleshy' green shoots and it will produce more of it from it and it keeps the plant low and productive.
If yours is already mature and 'woody'..just trim back all the 'greenery' as low as you can and leave leave some to re-grow...unless you use your rosemary regular basis, it will get pruned as you use it but you propably have to take bit more of than you would for your cooking..that way it will get gradually pruned and you have something to use as well all the time.