Here's what I've done in the past:
Get a stable, repeatable bike position setup:
Get a bike trainer that locks the rear wheel. This is a basic setup.
Use Rollers for a more advanced setup only when you want to measure pedaling mechanics and not just angles.
Use a camera:
Either find a good adjustable stand for your mobile phone, use a digital camera, or a GoPro. There are plenty of stand/brace options. You don't need a tripod. Maybe a barstool is enough. You need it to be at a repeatable height, maybe top tube height so as not to distort angles.
Keep the same zoom on the device. Changing zooms will change angles slightly.
Mount up:
Setup the bike such that you and the bike are in the center of the frame. Make sure that you are square to the camera and not angled off. You have to figure out a way to set repeatable cues like (tires on the bottom edge of the frame, top tube on the center line, x meters distance back from the bike...)
Record:
Record yourself pedaling at various cadences (even very slow). This is important. The slow speed is so that you can freeze frame and check your leg angles for comparison.
Check your race tuck.
Add resistance:
Add various levels of resistance and see if your posture changes adversely.
If you can, add enough resistance to simulate a standing start (if that's part of your event).
Download and Review.
Take screenshots of yourself and legs in various positions.
Look for "angle measurement software" for your computer and learn to measure your hip, leg, back and arm angles.
Compare
Now compare all of those to athletes who race the events you prefer and share a similar body type.
Google image search for your favorite athletes and SAVE THE PHOTOS. Use the angle measurement software to roughly measure the angles that they are using and compare them to yours.
I have dozens of videos like this, here is one example:
https://www.flickr.com/photos/carlet...l/12847821545/
This video helped me realize that my arms needed to be extended further out several centimeters. This is a 58cm frame and simply adding a 3cm longer stem would have adversely affected the handling. So, I had a 61cm frame built that kept the same handling but gave me the longer reach...which consequently lowered my back and made me more aero.
What techniques do you folks use?