I've done different things with mine, depending on what feels right. Usually when the ashes first come home, I put them somewhere with a favourite photo and candle and just wait until I know what to do next. Some of Charlie's ashes were scattered on his favourite beach, some on his favourite walk, and the rest we planted in a container with a silver birch tree and a remembrance plaque. Teddy's ashes are buried in the garden with a shrub and a plaque. I always have some sort of remembrance service, which might be a poem I've written, or one that seems appropriate, or just some words. Sometimes I've had several remembrance ceremonies.
I think it's important to do what feels right to you and not to feel any pressure to do anything right away. With Charlie's ashes, it took me 2 years before I knew what I wanted to do with them, but with Teddy's I knew very quickly.