If your fuel gauge and speedometer are not working on an all electronic/digital dashboard chances are you have a fuse that needs replaced or, you may need to check behind the dashboard for physical signs of water damage.
I suggest trying to change fuses first. Even all electronic cars like my Cadillac do well when I pull every fuse from the fuse panels and reinstall them. It doesn't hurt the on board computer as long as the car is not running while you're pulling them. Start the car after all have been replaced.
I have often found that doing this also helps things begin to work that may have been out of commission for a while as well. For NON-DIGITAL dash lights, simply check the light bulbs behind the speedometer and dash areas to examine the condition of the bulbs themselves. Often, moisture blows these bulbs out from condensation caused by temperature changes in the passenger compartment. Though you shouldn't have excessive moisture or you may have a leak that needs serious looking into. Keep all windows up at night.