I've been working on quite a few remodeling projects lately, and those include several bathrooms. Whether it be a powder room or master retreat, I'd like to share some of my basic DOs and DON'Ts that I always consider when approaching a design plan for these spaces.
Do get creative with tile.

[photo of the Hoxton Hotel via @mad_about_the_house]
This does not necessarily mean to follow the trends. Any room that is full of one trendy idea after another will quickly feel dated. Instead, focus on an interesting design that speaks to you. It may be some chic color blocking as pictured above, a patterned floor tile, or a unique way of installing a classic pattern. If there is a trend you like, by all means incorporate it, but mix in other classic elements to achieve a look that will have more longevity.
More bathrooms that use tile creatively...

[photo source unknown]

[photo via CTC&G]
Don't be afraid to use marble.

[photo via @jeremiahbrent]
Marble gets a bad rap. Because of its porous nature, it is more likely to stain. NEWS FLASH: All natural stones can stain. I am also of the belief that age and patina can add to the beauty of marble. It is one of the most luxurious materials one can use, and it lends itself to a variety of design styles. AND, because I am all about authenticity when choosing materials, I recommend steering clear of faux marble tile.
If marble is pushing you over budget, consider using it in a limited area such as the vanity countertop, or go a different route entirely. Though marble is fail-safe choice, there are many other beautiful options available.

[photo via House Beautiful]
Do take your shower tile all the way to the ceiling.

[photo via Rue Mag]
Nothing looks more unfinished than shower tile that stops about one foot below the ceiling. Taking your tile all the way up will not only elevate the look of your shower, but will draw the eye up making it appear taller and more spacious.
Don't highlight your tiny shampoo niche.
You create this spacious shower with beautiful tile and stunning shower fixtures only to draw your eye to a tiny square shampoo niche. To what purpose? That may not be the element to you want to feature, especially if you have created some other feature in your shower such as a band of accent tile. An accented niche will only distract from it. So unless you are creating a large architectural feature with your niche, it is best to have it blend in with the wall tile.
If you have your heart set on it, here are some shampoo niches done right...

[photo via Alison Giese Interiors]

[photo via Pinterest, source unknown]
You could instead try these options...
An accent wall or inlay in contrasting tile.

[left: photo via brit.co | right: photo via Pinterest, source unknown]
Highlighting your shower fixtures with a secondary material.

[left: photo via @in.house.design | right: photo via NYC&G]
Don't close off windows.

[photo via Bria Hammel Interiors]
There may be circumstances in which having a window in your bathroom is not possible, like if you live in an apartment building or townhouse. However, if given the option to have a window (or two), nothing beats having natural light in any space. This includes the bathroom.
Do mix metal finishes - with intention.

[left: BHDM Design | right: source unknown]
Mixing metals is a definite DO in design. I find it to be a concept most homeowners grapple with, but many designers embrace. The key is to make it look deliberate. I don't recommend mixing chrome and polished nickel as it will look like you made an attempt to match but weren't looking closely enough at your selections. Instead, choose one or two main fixtures, such as the vanity mirror, the faucet, or the cabinetry hardware in one accent finish, and keep all other fixtures (shower head, towel bar, etc.) in another finish. Combine chrome with matte black, brass with polished nickel. The mixture will feel fresh and add interest.
Happy renovating!
Lissette