Advantageously, you can use symmetry in your SolidWorks models to reduce the work required to create your detail. This also applies at the sketch level. As many probably already know, there is a tool for mirroring sketch geometry called "Mirror Enteties".
What many people probably do not know is that there is also a tool called "Dynamic Mirror" which gives the same result as "Mirror Enteties", however, the path to the goal is a little different. "Dynamic Mirror" reflects the sketch geometry directly when it is created and it is therefore not necessary to subsequently choose which geometry is to be mirrored over which axis.
Dynamic Mirror can be found under Tools -> Sketch Tools -> Dynamic Mirror. A prerequisite for the tool is that there is an axis to reflect the sketch geometry over which must also be specified when the tool is started. Once you have selected the mirror axis, which is identified via a pair of perpendicular lines at each end of the axis, you can then draw out your sketch geometry and see how it is mirrored directly without any extra keystrokes.
The two intersecting lines at each end indicate that it is the mirror axis
Geometry that I have drawn:
Geometry that is mirrored with "Dynamic Mirror":