Hi Anu,
GIF compression is usually used to compress Computer Generated Graphics like icons and clip arts.
JPEG compression is generally used to compress photographs.
Now there are several parameters that can influence compression.
For GIF files, compression is improved if you reduce the number of colors that composes the image. Computer Graphics usually contain few colors, that's why it is better.
If you are using mainly computer graphics, try to scale, re-arrange or reuse images accross the HTML page, to reach your goal.
For JPEG files, compression is improved if you decrease the quality factor (or compression factor). It is usually a value from 0 to 100 (0 = maximum compression, 100 = best compression).
You need to use a Imaging Editing Application to be able to set these parameters (or use an image processing API). For static images, I prefer to use Adobe Photoshop, but you might prefer PaintshopPro or some other tool.
For photographic pictures, JPEG gives the best compression. To give you an example, I am trying to compress a photograph of dolphins under
water whose size is 576x432 (I'm using Photoshop)
GIF 256 colors = 82K (quality of resulting image = OK)
GIF 128 colors = 60K (quality of resulting image = OK)
GIF 64 colors = 45K (quality of resulting image = poor)
GIF 32 colors = 31K (quality of resulting image = low)
GIF 16 colors = 22K (quality of resulting image = very low)
under that the image is difficult to see
JPEG 100% = 63K (quality of resulting image = perfect)
JPEG 80% = 31K (quality of resulting image = perfect)
JPEG 50% = 14K (quality of resulting image = near perfect)
JPEG 30% = 8K (quality of resulting image = OK)
JPEG 15% = 5.5K (quality of resulting image = poor)
JPEG 0% = 4K (quality of resulting image = low)
Hope this helps,