|Cranberry neck warmer|
If you knit tighter than you purl, or vise versa, your gauge will be different for the parts that are knitted in rows and the parts (or projects) that are knit in the round. You may find you need to use different sized needles for the same yarn but are used for different techniques used in projects.
Now, when you add colorwork, you may have to compensate for the gauge tightening then as well. Again, double check your gauge if you are adding colorwork to only one portion of your project.
Sometimes it helps to take a break, walk around a bit and wash your hands. I know when I knit in the warmer months things tend to get a bit slippery. I also tend to stay in my chair much longer than I should. Walking about every 1/2 hr helps you to stay focused.
And finally, try knitting your gauge swatch on different types of needles. Some yarns, such as chenille, are easier to knit on metal needles. Wool, on the other hand is easier to work (for me!) on wooden needles.