For practice, any size crochet hook and any type of yarn will do, so long as they are compatible in size (i.e. you’re not using a very small hook with thick yarn).
These instructions will assume you are right-handed; if you are left-handed, reverse them. To hold the hook, grasp it with your right hand as you would a pencil, resting it on the middle finger and holding it in place with the thumb. The yarn is going to be wound around your left fingers. First, make a slip knot near the end of the yarn: make a loop, and pull another loop through it. Tighten it, placing the hook inside (hook pointing away from end of yarn). It should be snug but not too tight.
Thread the yarn around the inside of your pinky, tip of the ring finger, loop once around the middle finger, and then over the index. The end will be held between your middle finger and thumb, just below where the hook meets the yarn. (Note: you may find an overhand grasp of the hook more comfortable, or choose to loop the yarn around your left hand differently. Experiment to see what works best for you.)
Understand that basic crochet fabric is made in rows. You’ll make one row of stitches, turn it around, make a second row on top of the first, turn it around again, make a third row, and so on. Therefore, when you make a base chain (described below), it should be as wide as you want your finished piece to be.
MAKING A BASE CHAIN.
All crochet fabric begins with a base chain. A base chain consists of chain stitches (“ch”) which are made by holding the yarn and hook as indicated above, swinging the hook over the yarn once (counter-clockwise) and pulling the yarn through. Make as many ch as you need, keeping in mind that one ch equals one single crochet stitch (don’t count the loop on the hook).
Tip: when you make a base chain, make the stitches bigger than you think they should be. They’ll look odd at first, but this will keep subsequent rows of fabric even. If your fabric pulls into a U shape, your base chain stitches need to be bigger, which means starting all over.
Add one more ch to your base chain, and place your hook through the second chain (top yarn only) from the hook. Wrap the yarn over the hook and pull it through the chain. Now you have two loops on the hook. “Yarn over” again, and pull it through both loops.
Congratulations! This is your first single crochet (“sc”) stitch. To make the next, place your hook in the next chain, yarn over, pull through, yarn over again, and pull through both loops. Continue to the end of the chain. When you get there, make one ch and turn your fabric around so the reverse side faces you.
The top of the row of sc you just made resembles the base chain. Place your hook at the top of the first sc and make another sc as described. Continue to the end, make one more ch, and turn the fabric around again. Continue like this until your piece is the size you desire. Snip off the yarn a couple of inches from the end, yarn over, and pull the loop/yarn all the way through, making a discreet knot. Use your crochet hook to weave both dangling ends through the fabric (an inch or so in is fine) and snip off any excess.
If you like, you can replace every other sc stitch with a ch for a more “openwork” feel. If you want to make stripes of color, start with color A, make a row (or two, or three, etc.) of stitches and finish off at the end as described above.
To add color B, make a slip knot at the end of the yarn as you normally would. Take the bare hook and poke it through the end of the fabric where you left off. Put the loop on the hook and pull it through. Voila! Now you can continue as you have before. After the desired number of rows, you can finish off and switch back to color A, or add color C.
Don’t be discouraged if your first attempts don’t look right; crochet takes practice. Strive to keep all your stitches even. When you notice a problem area, pull out the stitches immediately and do it over; you may think it won’t show if you let it slide, but it probably will. There shouldn’t be any gaping loops in your fabric, nor should it have a tight, puckered appearance. If your work seems too loose, you might want to try a smaller hook (and if it’s too tight, go a size larger).