Mother cat is almost ready to give birth. What indications do I look for and how do I prepare the birth area and should I give mother special food?

It depends on her... our cat gave out low growling sounds when she first went into labor and came to me for lots of love and affection... she made little growling sounds occasionally and I could see her stomach muscles working as they contracted. After a two or three hours, her first kitten was born on top of my bed.

She had been showing a lot of interest in the wardrobe in my room weeks prior to having her kittens, so my daughter and I had already prepared a space in there for her. We put down lots of newspaper and old sheets, so it was snug. Once the first kitten was born, we put her in the wardrobe, and in the morning found another two had been born through the night.

Not many cats behave like her, since mostly I've heard they disappear somewhere quiet and safe to have their kittens. The wardrobe in my room was ideal for her and kids from around the neighbourhood came by to see her and the kittens... it was a special time in our household, and I hope you enjoy it just as much :)

Mommy cat will take care of it all! I've gone through this when I was little, or younger.
When she starts having a different attitude, most likely she's in labour!
Now you can find a box and put some towels or blankets in it, but mommy will decide where she gives birth. They do like a very enclosed place that gives them privacy. DO NOT move her and/or her babies when she has found her spot and starts producing them.
When it's all over, mommy will take care of the babies. You really don't need to do much, be gentle with her and don't force her to do or eat anything she doesn't want to. Make sure she has water with her when she has her babies, and I'm not sure when it comes to food. It would be good to move her food and litter into the area she gives birth. This way she doesn't have to travel far when she needs to relieve herself.
I do state very strongly, talk to a vet about the best time to do so, but get her spayed! Mistakes happen, but there are already way too many unwanted dogs and cats in our world, we don't need more.
With cats and dogs, they know what to do when they have babies. Very few are lucky to have owner's who put them first and look for help with it!