Water Marbling

Sadly, these are probably my best attempt at water marbling. I used all Sinful Color nail polishes, which made water marbling so much easier. I had heard a tip that using all the same brand polish really helped, and boy was that correct. I'm not sure if others have this same problem but my biggest issue with water marbling is BY FAR my placement. I am always like, "Oh, this is the spot I want my nail to look like... do do do.... Dang it, how did I get my nail on top of the ugly spot right next to the pretty spot?" What's the hardest part of water marbling for you?