You can use a grid to work more precisely. You can also make it a magnetic grid (View menu > Snap to Grid) with a snap distance set in the General Preferences (> Snap).
After you have enabled the rulers you can drag guidelines from the ruler.
1. Choose View > Rulers to display the rulers. The rulers are displayed in the measurement unit defined in the Preferences.
2. Place your cursor on a ruler.
3. Drag a guideline from the ruler and release your mouse button if the guideline is in place.
4. Optional: If you want to use the guides as magnetic lines with a snap distance, choose View > Snap to Guides.
5. Optional: Double-click the guideline, if you want to define exact coordinates.
1. Choose View > Remove Guides.
2. Select the type(s) of guides which you want to remove.
3. Click OK.