To post large images effectively, using an image hosting site like ImageShack is recommended, as it allows for linking images in forum threads. Users should save images in formats like JPG or GIF to reduce file size, as BMP files are significantly larger. Understanding image compression and resolution is crucial; higher resolution images result in larger file sizes, while simpler images can be compressed more without losing quality. For optimal results, users should save images at the lowest quality that still meets their needs, balancing file size and visual clarity. Learning these skills can be achieved through experimentation and observing others' techniques.