To obtain the best results when knitting it is important
to knit a tension square before starting on your project.
If your pattern says that the gauge should be 17 stitches and 22 rows to a 10cm square on needles size 5mm then cast on 22 stitches using 5mm needles and knit stocking stitch, unless otherwise recommended to use the stitch in the pattern, back and forth over 26 rows in length.
Place a ruler on top of your swatch and count the number of stitches per 10 cm vertically and horizontally. If you have more then 17 stitches, the stitches are too small so try again with a bigger needle. If you have less 17 stitches, then the stitches are too big so try using a smaller needle.
Once you have established what needle to use you are ready to start. Remember however that it is a good idea to check your gauge several times whilst you are knitting.