When you are making something where you want the edge to remain even, don't crochet into the last stich of the previous row. Your chain will constitute as the last stitch.
Count your stiches after each row.
If you find your work is too loose, change to a smaller hook, if it is to tight, change to a bigger needle.
Patchwork and Applique
Closely woven fabrics are easier to handle and will give you the best results when making a patchwork
Using light weight and heavy weight fabrics together will cause the item to hang skew.
If you really want to mix light and heavy fabrics together for a particular desing, iron on some interfacing on the light fabrics to give them some weight.
Cottons and natural fabrics work best for patchworks as they are more predictable and do not stretch or shrink as much as synthetic fabrics might.