The best way to clean out that shower head is to pour vinegar into a plastic bag and fully submerge your shower head into it. Tie it in place and leave it overnight to soak. In the morning, you can remove the shower head and simply run your water through it to rinse it out.
Your shower curtains can get a great scrub too. All that you need to do is toss them into the washing machine with a few old towels to use as scrubbers. Add your usual laundry detergent to the mix and wash on hot. The towels will help to scrub off the soap scum and mildew from the curtains. Simply hang them back up to dry.
If you're facing the daunting task of cleaning shower doors, try making a paste of one cup of baking soda and a little white vinegar. You want to make sure that the consistency is thick and will cling to your shower doors. Let it sit for an hour and then rub with a microfiber cloth. Buff dry with a clean cloth after rinsing.