The best thing to do is turn down the resolution on your camera before you take your pictures. Read your manual, this is pretty easy to do. There is no sense it taking a photo greater than 3.5 megabytes when the one we show eBay buyers is 1/100th that size. Simply put we throw away extra pixels you don't need and keep only what we need to look great when supersized.
It seems like a shame to do a whole lot of extra work opening up paint, picasa, photoshop, and so on to resize your images manually when your camera will do that for you.
Set your camera to take the photo at 1600x1200 or the closest resolution to that. Most new cameras take pictures at 4000x3000 which is nearly 6x as many pixels and we just throw all that extra stuff away.
Increasing our size to a max of 3.5mb will help but some images on the newest cameras still save files larger than that. Looking through my digital camera files I see that at least 1 in 4 is larger than that. So unless I change my camera to use a lower resolution before taking photos I'm going to end up having to use paintshop or picasa, or some other image editor to resize them 1 at a time and that is just horrible to think about. I don't want to see anyone here having to do that work when your camera will do it for you with a few clicks.
On a Canon digital camera click Function Set button, then click down until the "L"(may also be M3,M2, or M1), then click right a few times. You should see the resolution show on the screen. On my camera M3 is 1600x1200. Once you on are on that click the Function set again. So literally like 4 or 5 clicks.
On my Camera:
L = 4000x3000 (12 megapixel)
M1 = 3264x2448 (8 megapixel)
M2 = 2592x1994 (5 megapixel)
M3 = 1600x1200 (2 megapixel)
So before taking photos I'd want to set it to either M2 or M3. M1 might work, but I think on rare cases it may still do a photo over 3.5 megs.