Depends on the size of the mug.
For every 100g of water, use 6g of coffee as a starting point.
My normal mug has 400g capacity so I use 24g of coffee normally *that can vary depending on the coffee used, but it's a damn good ratio to start with*
Check out
www.brewmethods.com for various brewing techniques.
Right, onto what I actually came in to post.
The excellent Brewista scales are now up for preorder at coffeehit with 10% off. They are really cool. Got to play with a set at the london coffee festival and have also tried them in a cafe in London. *said cafe has now ordered half a dozen of them, they were that impressed*
If you hang around on the main page of coffeehit you may also get another 10% off voucher code.
Still close to £40 for a set of scales admittedly, but given that I've spent nearly that on 4 sets of scales this year that die at the first hint of water, and these are pretty much waterproof, they look a good deal to me.