First there's a good set of flexible layout controls to build ui that'll position / size elements to the available screen real estate. So you can build screens

First there's a good set of flexible layout controls to build ui that'll position / size elements to the available screen real estate. So you can build screens that position elements fairly well on different resolutions. Second you can make multiple versions of these layouts that'll swap in given some device parameters. So if the flexible layouts didn't suit your need you could make (for example) one for tablets, one for phones. You can do the same for bitmaps so you can have different versions of each for different DPIs. For bitmap aspect ratio issues there are also 9patch bitmaps which specify which portions of the image can be stretched and which can't. That works pretty well for small adjustments and background images.