Plumbing repair is almost always best left to a professional, but some homeowners prefer to at least try to make their own repairs when it comes to the bath, or decide to handle a remodeling project on their own. It's true that kits for new bathtubs and shower repairs and online tutorial videos can make this work easier than ever before, but this doesn't mean a homeowner is not likely to make some mistakes with their bathroom repair work. Note a few of those there so you're sure to avoid them yourself.
Not getting parts meant for your pieces in particular
Any poorly-fitting part in the bathroom, including things as small as a washer or connector between pipes, will mean water leaks. Those pipes can also burst when water is running through and there is pressure on the pipes. The best way to avoid this mistake is to use parts that are meant for the pieces you have in the bathroom in particular; be sure you note the brand name of the shower kit you buy and the exact measurement of pipes.
Be sure to match the materials as well; plastic washers go with plastic pipes, and you should never put two different types of metal together as this can lead to early corrosion. Don't assume you can simply "make do" with an assortment of small parts, as you're sure to have leaks in the bathroom before too long if you do.
Not using plumber's tape
Even with properly fitting pieces, you still want to use plumber's tape around connectors. This tape goes on the outside of pipes, around the threads, and provides a waterproof seal between the pipe and the connector. Homeowners often forget to use this tape when installing new pipes or accessories so that they may have leaks behind the walls or from the showerhead itself.
Not waterproofing the job
If you go through a wall in the bathroom for any repair or renovation work, you want to ensure you add waterproofing back in place when you put the walls back up. This can mean plastic sheeting or protection around the pipes themselves. You also want to avoid using very porous materials for the bathroom including slate tiles or other such types of stones. If you do use these materials, you'll want to ensure they are sealed as often as recommended by the manufacturer. This will not only keep the inside of the walls dry but also protect them from damage if you overlook a leak inside the walls and which then seeps through the building materials.