First you must win a home and away auction. You will then receive a code (that is attached to your skyauction ID and can't be transferred) that you can use towards any future auction.
Before paying an invoice you either call them or email them and quote your skyauction user id and $100 home and away code. It may take a couple of days but they will apply this against your account. You then go ahead and pay the invoice with the adjusted amount.
Go to your account on skyauction and look under the refer a friend option. For each friend you refer (who actually joins, you earn $5 that you can put towards your next auction invoice). Max $50 per invoice. I used this last year, but unfortunately, I have run out of people to refer. But it made for cheap invoices ($100 home and away certificate plus $50 refer a friend skycash)!!!!!
Inventory looks weaker this year then last though on both ready set go and Home and away (getaway weeks). I have read that inventory is best about 2 months up until to the week before travel time, but due to having to book air, holidays at work etc., I always book several months ahead.