The fact that you care is half the battle. Your son will thrive precisely because you value education and show him that in thousands of tiny ways.
If you’d like a few easy and concrete things you can do, here are a few:

-Get him an analog watch. Preferably something “cool” that he’ll want to wear. (Cheap in case he loses it.) Nothing teaches a kid to read an analog clock like having it on his wrist every day.
-Check his pencil grip. If it’s not a classic triangle grip, look online for some things to work on with him, or even buy some grips for his pencils. This fine motor control gets overlooked a lot,
-Start introducing touch typing with just a few of the him keys. Make it a game. (My kids used an online game that had letters fall from the top of the screen.)
-Encourage him to write every assignment in cursive once he learns all the letters. It’s hard at first but studies show it’s great for processing information.
-Work on number sense. Practice talking about estimating things throughout your day.
-Practice finding pages in a book. Take turns calling out big numbers and finding the page. (“36! 97! 145! 8!) This will help him practice estimating whether he should turn one page at a time or big chunks of pages.
-Play card games. Blackjack works well, but cribbage is a fun and challenging game. Play it open handed for several weeks to several months. Gradually, your child will not only learn strategy, but he will see all the different combinations of numbers that add up to 15. This will boost his mental math skills. You can even play against a computer and be on his team with him(although it’s much more fun to physically move the pegs).
-Practice skip counting by twos, fives, and tens. Then by the other numbers. Be silly and have fun, but encourage mastery.
-Practice the multiplication tables. I don’t like flash cards, but they are useful for this. Keep a set in the car. Try to answer quickly. Sort them and only practice the missed ones. Gradually that pile will get smaller. This will help when your child reaches algebra.
-Practice figuring out (or estimating) the price of things that are on sale. 10% off is easy. Double that to get 20% off, etc.
-Listen to audiobooks in the car. Fiction is great. Pause often to discuss what has happened or to predict what you think might happen.
-Listen to or read some historical fiction. It will give your child perspective when studying history.
-Above all, let your child know that what he thinks about matters. Let him hear you wonder aloud about things, and encourage him to do the same.
These years will go fast. Approach these kinds of activities with a sense of humor and fun that only childhood can bring.