Just as a disclaimer I guess, just tell me the generic distances and steps. I know my horse will be different than all of yours and everything, just want to know a good rule of thumb when setting jumps!
Are you doing vertical to vertical? An oxer to a vertical? Oxer to a vertical will make a standard distance feel a little short. Make sure if you do an oxer first that you're measuring the distance from the back rail to the next jump, not front rail to front rail.
Edit: Also it depends on how you have to approach the combination. Coming 2-3 strides out of a corner to the first jump will probably make a distance feel longer since coming around that corner can make you lose some power if you're not keeping up on your tempo and stride. My coach recently set up a triple combination (oxer, two strides, vertical, one stride, big boxes) and even though the oxer was first you had to move along to get that two strides in, and then had to steady through the one so you didn't get too close to the third effort.
Edit again: Distances, sorry I forgot! A one stride is 24 ft, two stride is 36 ft. If you're in an indoor make them a foot or two short, because the standard distances will ride long when you're in an indoor arena.