What is the best footing for clay soil that is sloping (starting higher and sloping down)? I tried concrete blocks but it was a disaster trying to level it. I am a newbie and have never done this before.
Welcome to the Bunnings Workshop community @janga892. It's fantastic to have you join us and many thanks for your question.
What footings you need to use are dependant on your soil classification. A geotechnical engineer will take several samples from your site and determine what classification the soil is. A structural engineer can then determine what sort of footing system is suitable for your site and deck.
I'm not sure how you are using concrete blocks in this scenario but generally, a footer would be a hole dug into the ground to a depth suitable for your soil type at a minimum of 300mm diameter. A post would then be concreted into that hole and backfill added which is compacted.
If you have had issues with the soil before I would encourage to speak with your local council as they might have an in house permit surveyor you could work with.