Everybody used to homeschool preschool and you still can. Get a preschool workbook from just about anywhere and pair it with lots of hands-on fun like alphabet games, puzzles, art projects, crafts, cooking in the kitchen with Dad. Then add in a once-a-week play group with other little ones.
To be ready for 1st grade kids should know the ABC's, being able to identify letters and sounds, be able to count to 30 or higher and recognize the numbers, be able to identify the major colors and shapes, and be read to lots and lots. It's also fun to include other preschool topics just to keep little ones interested in learning about their world.
Playing is not just fun, it is how kids learn. They copy their elders and this becomes pretending, dressing up, and "stories". They build, dig, and climb and this becomes gross motor control. They scribble, pretend to write, pick up little pieces, and sort and this becomes fine motor control. Most of this play-to-learn happens spontaneously, but sometimes teaching a new game or teaching a new skill can broaden a child's experiences past where they would venture on their own.