Well, who do you call on? Just 'God' and' Goddess'? Or is there a certain deity you visualize or think of? If you are drawn to a certain deity, try researching them and figure out what they would like [regarding animal sacrifice I would go with some type of symbolic offering or meat from a butcher over killing an animal]
If you just want to say thank you but have no clue what deity you have been speaking with [you should look into asking them their name] you could give incense, light a new candle, make something like a painting or necklace. If you have a permanent altar you can place flowers or seasonal decorations on it [colourful leaves and acorns for autumn] food and drink are always welcome. Again, depending on the deity you might find certain foods better than others. My goddess is associated with the harvest [among other things] so I offer a lot of fresh fruits and vegetables. Most mornings I have a fruit salad with breakfast so I set some aside for an offering. Today it was raspberries, yesterday an apple, before that blueberries. You'll discover over times what is favoured.
Another thing you can do that many people I speak with do is live in a way you make your God and Goddess proud. One person I watch works with the Morrigan, who is loving but can give you a good slap if you deserve it [or so I'm told] to connect with the Morrigan this person volunteers every month at a woman's shelter. An example at her behavior she gave in a video was if she's out in the park and some kid isn't paying attention and runs across her picnic blanket, her response would be stern but fair, because that's what her Goddess would do. Granted, that's not an excuse to harm someone because you worship a God of war or whatever, but you should stop and ask yourself 'how would my Goddess or God act in this situation' because we are all part of the divine.