No particular conventions in my field
if your article is similar to the last one, maybe the same journal is fine, or if you think you could get higher impact, then go for it.
There is'nt really such a thing as publishing etiquette, it's not like journals have feelings or anything, as a general rule aim to submit to the best journal you think might accept your article. Obviously if its the same article, you can only have it published once, but you probably already know that.