Resize without distortion
Keep 'Lock aspect ratio' on and set just the width or height; Aimager calculates the other side automatically so your image never looks squashed. Unlock it only when you deliberately need exact non-proportional dimensions.
Percentage and presets
Percentage resizing (25%, 50%, 75%) is the quickest way to make an image smaller by a known amount. Downscaling also reduces file size significantly, which pairs well with compression.