Index
Content
Placement
Style
Art
Packaging
5. Packaging
5.1) Image Properties
It helps if you have a viewer that lets you see some of the image properties as you view. ACDSee for example shows you, among others, the filename, filesize, image dimensions, image depth, etc. Anyway, make sure that image dimensions (height and/or width) and depth are consistent--pngs should all be uninterlaced and the same bitrate (either all 4bit or all 8bit, not some of each, and never more than 8bit).
Additionally, make sure the files are named properly. Make sure the filenames are consistent and informative. Make sure you include leading 0's when needed (01, 02, 03, ... 09, 10, ... not 1, 10, ... 19, 2, 20, ... ) so images are viewed in order. If you use TweakUI for Windows XP, one of the settings in "Explorer" is "use intuitive filename sorting"; uncheck this so you don't get confused. Make sure that pages are in order when sorted by either filename or filetype. Make sure, when applicable, that numbers in the filename match up with numbers printed on the page.
Make sure filesizes are reasonable--png's for a 1200px height image should usually be 100-300KB, jpg's for black&white should be about the same, and color pages should typically be 300-600. Cover pages will typically be bigger since they'll usually be wider, and spreads will obviously be roughly double these sizes. These are just approximate of course, there's no need to change anything if it's within a reasonable range.
5.2) Archive Properties
Make sure your files are packaged in zip, not rar, cbr, or cbz (see here for why). Make sure the name of the zip is consistent, and whether or not images are directly in the zip or within a folder in the zip. Make sure you get rid of the thumbs.db file. Make sure the filesize is respectable (a 20pg chapter with no color pages, 1200px height, should be ~3-4MB).
Pay special attention if you use spaces in your filenames. IRC distro will usually convert spaces to underscores, so it's generally preferable to go ahead and just use underscores instead. Plus, sometimes single spaces may be overlooked, or you may accidentally put a double space where there should only be one. Just be careful.
5.3) Extras
I don't think fanart belongs in manga scanslations, ugly or beautiful. If you absolutely must show off your best friend's sketches or attempts at coloring some random page, put it in a subdirectory. Also, use a bit of discretion, and don't put too much in there. A nice example of too much would be some of AQS's recent Negima releases--not only are the pages huge (8+mb for 19pgs), but there was almost 5mb of "extras" packaged with the release. That's an entire chapter's worth (a properly cleaned and compressed chapter). If you absolutely insist on putting it in, don't go overboard.
At most, put 1 credits page per chapter. Who did the work, any special acknowledgements, general comments, translation notes, etc. should go on one page (or in margins/blank space of manga pages). Sometimes, for special notes that are included for a specific chapter, you can put another page, but this shouldn't be for every chapter.
Index
Content
Placement
Style
Art
Packaging