Marble swirls are another kind of nail art you can do that looks harder than it actually is (and also a lot less messy than water marble).
All you need to do is blob on your polish and swirl the polishes together (still wet) with a cocktail stick or bobby pin or a dotting tool. Some nails can turn out not as great as other nails (a couple of mines had some bare patches I didn't notice till later) but I think it's nice that not all nails are the same or uniform within themselves!
Models Own Hypergel: Purple Gleam
Models Own Scented: Peach Melba