There is nothing more frustrating than to count your stitches after making decreases or increases and realize that you are missing or have more stitches than what the pattern calls for. This is why is a good idea to use a lifeline. At first, you might feel lifelines are tedious or time consuming (like when you are working on that first gauge swatch), you wished you didn't have to do it. I am sorry to tell you that you have to. You must do it if you want to save time later.
A lifeline is a piece of thread that you can run with a tapestry needle through a row of stitches as a placeholder in case you have to go back a few rows and fix a dropped stitch or fix a mistake. Lifelines are a lifesaver when you work in lace patterns or when you work with a lot of stitches. They will prevent ripping back rows of hard work and precious time.
You tube is great source for tutorials but one of my favorites is this video where 3 different ways of inserting the lifeline are demonstrated by Michelle Hunter
Things to remember:
1-Move your lifeline up as you make progress. When working a complicated lace pattern, move the lifeline as needed like every repeat or every 5 rows depending on how complicated the pattern is. 2-When working on decreases or increases or adding color work, use your judgements and move the lifeline as needed. 3-I like to use bright colors in a lightweight yarn as a lifeline. In case of an emergency, dental floss works perfect.
Don't forget to keep knitting everyday!