The best tips I can give you are to make sure your listings finish between 6 and 8pm, as statistically this is when you are likely to get most hits and bidding wars.
If you are buying, look for listings that finish in the middle of the night 
Be as detailed as possible in listings, make sure to offer more photos if required and basically be as amenable as possible got your potential buyers.
I always offer a cash on collection option and if you have any negative feedback (like I have) always offer an explanation why and ask buyers to contact you before leaving neg/neutral feedback.
State on your listing when you anticipate sending items out. I post out on a Tuesday and a Friday only and state this - but if someone wants something quicker I will endeavour to get the item out as soon as cleared payment is received.
Doing this gives buyers a clear instruction and you a bit of leeway if you can't do the packing and posting immediately!
If you've got a lot of stuff to list, try and make your listing finish just after lunch on a Saturday, that way, the earliest you can post out is Monday morning, giving you time to package up and address stuff, plus, if your buyers haven't paid by Monday morning, you've also got good enough reason to chase for payment! I always ask for payment via paypal or contact to arrange collection within 24 hours auction end. If this doesn't happen and I haven't received payment after 3 days, eBay automatically opens an unpaid item case for me! Saves me having to mess about with chasing people and opening cases!!
Hope some of this helps you!!! Good luck!!!