Do you mean that you're not happy with the way the vertices are getting laid out?
If so and if you are using a FruchtermanReingoldLayout object, you can increase its "Iterations" property from its default value of 10. This property determines how many times the algorithm runs--larger values result in vertices getting shoved further
apart. Here is a description from the NodeXLApi help file:
The number of times to run the Fruchterman-Reingold algorithm when the graph is laid out, as an Int32. Must be greater than zero. The default value is 10.
The FruchtermanReingoldLayout class also has a "C" property that determines the strength of repulsive and attractive forces. (It's called "C" because that's the name Fruchterman and Reingold used in their research paper.) From the help file:
The "C" constant in the "Modelling the forces" section of the Fruchterman-Reingold paper. Must be greater than 0. The default value is 1.0.
Increasing C decreases the attractive forces and increases the repulsive forces; decreasing C increases the attractive forces and decreases the repulsive forces.
There are no hard-and-fast rules concerning how you should set these. If you have the NodeXL Excel Template, you can use it to experiment with different values. In the Template, the values are available at NodeXL, Graph, Layout, Layout Options.