jducoeur

Skylights are a huge energy problem most of the year. They let in too much heat in the summer, and let out too much in the winter. You can cover them with something solid like opaque canvas outside, or with reflecting films inside. Don't bother with anything inside which isn't touching the glass.

Which direction do the windows face? West windows are your biggest problem for heat input. Shade them if you can. Growing hops up strings works nicely and gets you hops(!). South windows if appropriately overhung shouldn't be letting in much sun.

For days when it is a reasonable temperature outside, open high windows on the downwind side and twice that size of low ones on the upwind side. Augment with fans as needed (blow in on the low side, out on the high). Opening too many windows is counterproductive.

Make sure ceiling fans are set to blow air down. Only use them in rooms where you are currently residing.

A small fan directly blowing on you will cool you immensely.

For days when it is too hot outside, close the windows in the morning and open them after it has cooled off at night. Blow air up from the basement (make sure this doesn't create too much of a moisture problem in the basement).

Refrain from doing anything which produces moisture (showers, boiling water, etc.)

Put the big machines in the basement. A laptop only, on your desk.

Don't run the hot dry cycle on the dishwasher (or dryer), and run it only when it is cool.

CFLs.

If you do run the AC, use it only in the room you are in, if you can.