In a typical pushrod setup, there's an adjustable clevis on one end, and a Z-bend on the other.

For park flyers, Dubro EZ Connectors make it very simple. I would not suggest using them for primary control surfaces on anything but small park fliers.

You could also put Z-bends in both ends, but this requires a high level of precision, and does not allow you to make adjustments later. A variation on this method involves bending a large V into the pushrod along an open unobstructed section of the rod, then putting Z-bends in both ends. By widening or narrowing the V, you can adjust the length of the pushrod:

z----------v-----z

This should also be limited to small park flyers, because the V can induce some unpredictable flexing when used on a heavier airplane.