hah, I thought I was the only one that did this! Though my usual go to dream-starter is either flight, or snowboarding.

With flight, I just imagine that I'm flying relatively low above the tree line (Iron Man style with my hands at my side, rather than Superman style with arms outstretched ... not sure why, but this matters to my brain :P ). Also, I start somewhere that I'm really familiar with such as my house or office and then I make sure to not follow the roads ... the thought of flying across blocks and lakes really makes me happy.

With snowboarding, I just imagine myself at the peak of a gigantic mountain. The terrain oscillates somewhere between greens and blues and is a chill winding experience.