Saying Thank you goes a long way. I don't leave food offerings, one of my pets would just eat it. I leave a chalice of water outside which is imbued with my own energy and I ask the deity to come and partake if they wish to do so. When it has been left a while I thank the deity again and ask that they take their leave when they wish and then I pour the water over a tree which I planted myself....
There are MANY ways to thank a deity, the above is something I do because it is convenient.