When you say it gets smaller, do you mean that your piece is getting narrower? If so, it may be a turning chain issue.
If you are not making a turning chain, then that is probably the issue. A turning chain is when you crochet extra stitches to begin the next row at the correct height for the stitch you are using.
Your turning chain may not be long enough and could be pulling the work in. You might need to make it another stitch longer to make it work. (I vary how long my turning chain is depending on the weight of the yarn, but for double crochet, for example, I usually make a four stitch turning chain, not three as most patterns call for.)
You may also be crocheting into the top of the turning chain at the end of your row and accidentally not counting it as a stitch. I suggest that you count your stitches. If you have fewer stitches on each row, then it probably is a turning chain issue.
I don't know of any videos, but you might take a look at these pages:
Turning your work