A Dozen Centered Squares
Here are twelve ways to draw a square centered on the origin. In SolidWorks 2008 there is a dedicated tool to accomplish this. But let's say you don't have a specialized tool. Even for something basic like a square there are lots of ways of getting it done. Sure, some of them may be overly complicated for the task at hand, but keep in mind: if it doesn't work, there are always options. The complicated ones may come in handy.
I usually use option 3, as you can also make it work for rectangles by deleting the equal relationship.
1. Fully Dimensioned
Basic construction using 4 dimensions and 4 constraints. To change the size of the square required 4 edits.
2. Link Values and Equations
Same basic construction, but now I'm linking everything to a link value called "size" which drives the size of the square with one edit.
3. Diagonal Midpoint
Draw a rectangle, make two sides equal. Connect a diagonal construction line, and constrain to origin using Midpoint relationship.
4. Polygon
A square is a 4-sided polygon, so use the polygon tool on the origin, a horizontal constraint and a dimension.
5. Parallelogram
A square is also a right-angled parallelogram, so use the parallelogram tool with two perpendicular corners at the bottom. Draw a construction line connecting the side midpoints, constrain the center of the construction line to the origin.
6. Four Equal Line Midpoints
Use two centerlines and four equal lines, two midpoints, and some horizontal constraints (or something like that) to build up the square. Looks to me now that there are some unnecessary relations in this sketch.
7. Quadrant Pattern
This is shown incomplete. You can draw up one quadrant, use an equal relation and apply a circular sketch pattern. Note, this will result in 8 sides, not 4.
8. Side Pattern
By applying another dimension and a midpoint relation we could set this up to apply a circular sketch pattern and end up with 4 sides.
9. Side Pattern with Single Dimension
By utilizing the diagonals and a horizontal constraint, you could circular pattern a side with a single dimension.
10. Dynamic Mirror across Diagonal
You could draw a centerline, midpoint position it, relate it by angle to a reference plane ("Top" here), turn on dynamic mirror and draw a horizontal and vertical line.
11. Mirror Complete
This gets a little hairy to avoid using a second dimension. By using a center and a construction line, making them equal, aligning the end of the side to the horizontal line, then doing mirror across the horizontal, you could create a square. Draw the two verticals (no relations required) to complete the square.
12. No Relationships
Since the last one seemed to have a lot of relationships, here is one sketch that does not require any relationships. By using link values and equations you can still edit this by changing a single number. The 90 degrees on the left side are dimensioned to the Top reference plane