If you write them wrong you will catch hell, and if you don't write them all you'll still catch hell.
Here are some tips.
The hardest thing is balancing the fact that you don't want to hide a characters minority status but you don't want to push it into stereotype or tokenism territory. A character's race, gender, or sexuality needs to be part of their identity, but not the entirety of their identity. The audience needs get the vibe that all the characters know about the diversity of the cast, but don't care about it. It should only be a factor when it's pertinent, which brings up the hard part, writing a scene where the diversity is pertinant with out looking like your trying to say something about it. In a lot of ways it's like flirting. The moment you explicitly start talking about it you have lost your audience, or have probably something stupid that you should have been smacked for. You have to write about race without seeming like your're writing about race.
First off visual stereotypes are a big no no. But behavioral stereotypes are a little murkier and again you need to be subtle. There was a long time I didn't listen to rap because I was afraid of being taken as a gang banger. Then in my freshmen year in college I discovered Common. You can't be afraid of showing black people taking part of in certain activities, but if you are it has to feel organic. Again it has to be subtlety part of something the character will do. The Wire is full of drug selling gangbangers but is often regarded as one of the best handling of race on television in years. It had balls. No matter what happened the audience always knew characters came first. A character's not brandishing a weapon and slingin' coke because the writers are lazy and thought black guy = drug dealer. It's the opposite the writers deliberately mapped out the characters and the setting.
By the way the subtlety of the wire is why I can't watch Law and Order SVU with out cursing.
How storytellers portrayed various minorities over time has a lot to do with what the writers thought and not what was reality. We need to break from those and try to portray reality, with acceptable breaks due to comedy.
Be careful of what you don't show
Just as important of what you write is what you don't. If you're writing a civil war epic you might want to even passingly make a mention of slavery. A picture about 1950's/60's Alabama. Maybe take a moment to show the characters talking around a newspaper. As much as I hate to admit it that's why we have Black History Month, because in a lot of the retelling of history black folks and events involving black folks gets just plain left out. It sends the subtle message that we weren't there. Same goes for other minorities. If you're doing a WWII piece make mention of the female factory workers and nurses.
Don't Have an Agenda
The thing that really pisses me of is when writers, try to use race to pass along some message to the audience. Well meaning or not it most of the time turns into horrendous writing.