- He's very right about previewing on the device. I like xScope better than Silkscreen, because it can stream anything, both file, or screen region, and overall it's a nice designer's utility belt. There's nothing like that for android, at least I haven't found anything that works, and Android needs this even more, because it usually uses OLED, not LED screens.
- Unless you have plenty of time and very little UI, you shouldn't optimise for @1x design. The key is to design @2x assets that are ALWAYS even. Everything has to be 2 pixels or even-sized, every line, button size, coordinate and so on. To achieve crisp, 1px lines on Retina, you can do 1px strokes (for example, on button), but you have to make sure they are inside evenly sized (round-)rect, and twice as "strong" (darker, lighter, etc.), so that when PhotoShop resizes that 1px line, its darkness is mixed with the next pixel inside the button, and looks right on standard resolution.
- Another app I highly recommend: Slicy. Saved me many hours of work, and can automate the whole process of exporting assets.
- Keep the asset naming consistent, that will make developers happier and more productive.
- Learn at least the basics of iOS and Android app development. Basics are easy, and you will learn how developers layout the interfaces. That will get you thinking while designing, what assets will allow developers to make the design easiest and simplest to implement. In many cases, a well-prepared PNG can save many lines of code.