What is a good way to increase the speed of my 1.5 year old MacBook?

First clean your computer than probably increasing RAM would be the best thing to do and you can try overclocking too(I don’t now if is possible on Apple products but you can do a little research).

More RAM if you can. It makes a huge difference.

Tie a brick to it and drop it out a high window.

If you launch “activity monitor” (look in the utilities folder), you can see which apps are hogging up the CPU and how much RAM is allocated to them… Then try not to use too many of those apps together.
As stated above, max out the RAM. also a better place for answers may be the discussions area on Apple’s site. Goodluck

more ram, yes..

also, snow leopard is coming out, and this should speed things up a bit as well.

tie it to your zonda with a long rope and pull it behind you at 300 km/h over the tarmac