1/ Let them see you reading and read to them often
If your preschooler sees you reading he will assume it is something all grown-ups do regularly and want to join in. Likewise if you spend time each day reading to him, he will view it as an everyday activity and look forward to the special attention. From an early age it is important to associate reading with pleasurable things.
2/ Teach him to count to 10
Repetition helps the brain develop so learning to count is important. You can count out loud when playing with your child, play number games in the bath, point out numbers on objects when you are out and about with your little one.
3/ Help him learn basic motor skills
This will definitely give him a head start in kindergarten. It could include activities such as throwing a ball, coloring with crayons or pencils or cutting out with scissors. Making cards for grandparents or friends is a great example of this as it could involve cutting, folding, coloring and gluing.
4/ Teach shapes and colors
Coordination skills are important, so games like putting the correct shapes in the right holes are perfect to teach this skill. The shapes are usually different colors too so you can develop both these skills at the same time.
5/ Teach spatial relationships
Meaning opposites, such as under and over, in and out etc. You could devise a game with cuddly toys and ask questions like: "Is teddy under the bed or on the bed?", "Is doggy inside the box or outside the box?" You get the idea!?
6/ Teach him to say the alphabet
A simple rhyming song is great for this. There are many to choose from, and if you can't think of one just make it up. My mother had a wonderful way of teaching my siblings and I to say and recognise the letters of the alphabet. Every day she would draw a letter on a piece of white card and we would paint it or color it in. When it had dried she would help us to cut it out and then it was hung on the kitchen wall.
7/ Teach him to recognise a few letters
Some useful ones like the letters in his name would be a great start. That way he can recognise things with his name on in school.
8/ Teach him to sort objects
It is a good skill to learn at an early age. You can use opportunities such as when folding the laundry to teach your child to sort socks. Or when putting away groceries, to put all the cans together, all the cereal or all the juice boxes. Candy can be a good tool too, such as with a packet of M&M's, he could separate all the colors.
9/ Use good grammar
If you don't personally have good grammar then it is worth checking some books out of the library and teaching yourself. You are your child's best example and he will imitate you. It is a great start for your child if he learns it correctly the first time.
10/ Use a varied vocabulary
Again this will give your child a huge advantage in school. William Shakespeare had a vocabulary of over 21,000 words, but the average person's today is just 2000, rising to 3000 / 4000 for a university graduate. Having a wide vocabulary helps your preschooler prepare for his future very early on.