Place a series of cameras that look along a path.
To see the path, enable "Cameras and path" in the camera dialog.
Depending on the speed of flythrough and the sinuousity of the path, you might have 10 frames between key frame cameras or up to 30 or more.
Each camera must be tweaked to achieve a smooth path - look out for back and forth targeting - makes viewers dizzy. Archicad cameras do not accelerate or decelerate in their path easily. Your flythroughs should crossfade in a video editing application for smoothness.
As for generating the fly-through, experiment with OpenGL views to get the framing and path correct, and depending on the power of your setup, a 360x240 pixel Rendering is not a bad starting size. Use wireframe viiew for speed in checking the path.
Always save as individual uncompressed frames for ease of replacing bad frames - save later to a movie in Quicktime Pro.