4-minutes is plenty
Try to reduce the time you spend showering by using a shower timer. You can get sand timers and electronic timers. Alternatively, just choose your favourite 4-minute song from this playlist.
Collect and re-use
Use a bucket to collect water while waiting for the shower to get hot. You can use this excess water to water your plants. You can even put the plug in for the duration of your shower, if your not using any particularly harsh soaps or products, and then give your houseplants a dip once your ex-shower water has cooled.
On and Off again
Turn off the shower in between rinsing where possible such as when applying shampoo, shaving your legs or brushing your teeth.