Tunisian crochet requires a bigger hook than regular crochet or knitting (ignore the yarn band!). A good rule of thumb is to go up at least 2 hook sizes.
What happens if you are using a size too small? The fabric will curl A LOT. If your fabric is curling more than can be easily blocked out, you need to try a larger hook. The fabric is also really dense. You should be able to easily insert your hook. If you're struggling, the fabric is too dense and you need to try a larger hook.
Where to start? If you're working with sock/fingering yarn, try a 5.0mm (H) hook. DK? Try a 6.5mm(K) hook. If you've tried tunisian crochet before and did not like the fabric, it could have been you were using a hook that was too small.
Tunisian crochet makes blending yarn very easy. When making any project using two or more skeins of the same color you'll want to blend them so the transitions are not obvious. You can also use this technique for making a gradual fade between skeins of different colors.
To do this, simply swap between the skeins at the beginning of the return pass. When you finish the forward pass, drop the active color and pick up the new color and work the return pass as instructed. Do this on every row for a few rows and the transition will be almost seamless because each row has color from both skeins as illustrated in the last three rows of the photo below.
One of the questions I am frequently asked is "What length cable do I need?". The answer is mostly up to personal preference. If you don't mind a lot of stitches bunched together then a very short cable will work just fine. If the project has any corners (like a center out triangle shawl), then a longer cable will be more comfortable. My most commonly used cables are 1" and 8". Below is a 6" (15cm) hook with 1" (2.5cm) cable with a 150 stitch row.