When you increase in a lace pattern, you kind of have to 'wing it' to maintain the extra stitches in pattern.
What I like to do is to keep a center stitch in stockinette, almost like a fake seam and do my increases on each side of that.
So let's say that the X is your center seam, and your pattern stitches are l-9. When you increase, you'll expand out from the X
. . . . . . . . . 1 X 1 . . . . . . .
. . . . . . .. 2 1 X 1 2
.............3 2 1 X 1 2 3
and so on.
With lace, though, you have yo's and dec to consider. So what you have to do is only do a dec if you have a yo to balance it and vice versa, so you'd just work the stitches in question as stockinette.
Also, you can use a yo without a corresponding dec and use that as your increase on that row if it works out to do so.
I find that it's easy to work the increases at the end of the rows, because you're continuing in pattern and just adding one at the end.
However, when you have to increase at the beginning of the row, you have to count back from the first stitch of your first full repeat to see where you need to start the pattern. After a while, though, you can see it. Once you get enough stitches for a full repeat, you start the process over again.
Don't worry if you 'mess up' on a row or two with adding a yo or making a dec. As long as the pattern lines up, you can compensate later and add or not add a stitch to end up with the right number.
Or you can have a stockinette strip and call it correct.