Cut your poster board into 6" x 22" cards. You can do it yourself the slow way using scissors. Or, if you have one, use a paper cutter. Copy and print stores often have paper cutters available for use by the public. A local print shop may cut it for you for a price. Or you can skip this step and buy it precut at Gentle Revolution Press (link below).
Choose the words that you want to teach your baby. Begin with words about his or her world starting with his or her body and family, then home and interests. Use nouns, verbs and adjectives - the rest he'll pick up in context. This helps avoid boredom. Don't shy away from long words. If all the words are short, three-letter words it will quickly become boring for your child. Mix them up! And make at least 100 word cards before starting your baby's reading program.
Use your big fat red marker to neatly print the words on the shiny side of your cards. The size of the print is crucial to your success. Infants have immature visual pathways. If the print is too small they get frustrated because they have to work so hard to see the words. If you and I had to read words that were too small we might not want to read either. Imagine having to read everything in a 6 point font!
Use lower case letters, unless the word is a proper noun, leaving a one-inch margin around the words. Your finished product should have large 4" tall words on them. That way when you are showing them your baby your fingers will not obscure any parts of the letters.
Don't worry if you think your handwriting is not neat enough. All babies are extremely smart when it comes to language and will be able to learn your handwriting and then transition to type-set letters.
The back side of the card is your side. At the center top edge, using a pen write the same word again big enough for you to read quickly. Write "Date" on the left side. This will be where you will write the date that you began showing that particular word to your child. Leave the right side blank so that you can make hash marks to record how many times you've shown the card.
Some parents like to laminate their word cards if they anticipate having more than one baby to teach. But this step is completely optional. I've used the same unlaminated, word cards with three babies and they are still fine. Just don't let your baby play with them if you plan to use them again.