If people only wrote from personal experience, there would be no fiction worth reading. The issue of including people of different colours and other characteristics is something many authors never consider. I applaud you for recognizing that there are many different people out there and being willing to include them. The default for most people in North America and Europe when a character is not described is that they are white, heterosexual and able bodied. Don't worry about offending anyone, the greatest offence is in not including any of us with greater amounts of pigment in our skin or other ways groups of people differ.
To me the easiest way for you to start doing this is to write your characters and story, and then make some of them different colours, ethnicities, orientations, abilities, etc. A black man born and raised in Chicago has more in common with a white man from the same place than he does with a black man born and raised in Kenya. A man and a woman who are deaf have something prominent in common, but in other ways they can be vastly different.
Don’t be afraid of descriptions. The colour, type, size and age of a car is routinely mentioned; why not the same for people? You can have a light blue, four door, and five year old door sedan driving down a busy street. You can have a dark brown, thin, 45 year old New Yorker going down the sidewalk in his wheelchair. There is nothing offensive with stating a person’s appearance.
The characteristics don’t have to impact the story. E.g. Police Detective Henry Grange kisses his husband goodbye as he leaves to investigate a triple homicide- The fact that Detective Henry is homosexual may never come into play in the story. So why put it in? So someone who is homosexual can see something of themselves as a strong character and someone who is not homosexual to see that they can do the things heterosexual people do. The same goes for colour, gender and other characteristics.
In the book The Shawshank Redemption the character of Ellis Redding (Red) is white, in the movie he is played by black actor Morgan Freeman. Did it matter what colour he was in terms of how he behaved, no. It mattered in that he was included. People, especially youth, want and need to see themselves represented. If you want to contain cultural references for those characters then do a little research, talk to people and find some that are realistic for your characters to have or do. The same goes for any issues you want to have in your story.
My feeling is if a person wants diverse people to read their book, it would help to have diverse characters in their book. The harder task is incorporating the description into the story in a way that feels natural. Good luck with your writing.
