Determining reflection points

FIRST REFLECTION POINTS :

Speaker angle is irrelevant.
Tweeter > Side Wall(s) > Listening Position ( ear level ),
Tweeter > Ceiling > Listening position,
Tweeter > Floor > Listening Position.
The easiest way to find 1st reflection points is to use a mirror. Seat in your listening position while another person slides a mirror ( small, about 4"x4" ) along the side wall until you can clearly see speaker's tweeter. NOW you have your 1st reflection point. Same procedure for remaining wall and ceiling ( I am assuming you already have rug or carpet on you floor )

Mrjstark is correct for most speakers, and correct about the mirror technique.

Note that line-source speakers don't have a significant floor and ceiling first reflection. Note that bipoles and dipoles will have a significant first reflection off of the wall behind the speaker. And if the speakers have a well-controlled radiation pattern, it's possible that enough toe-in could essentially avoid the first near-side-wall reflection.

Duke

Thank you Mrjstark. That makes it easier.
And thank you Duke. That may make it even easier. As always Duke, you rock!

YES "Audiokinesis", dipoles are exception ( rear wall seams to play far more important role in setting up those kind of speakers then reflection points on side walls). Speakers with very small radiation pattern are indeed less affected by side walls sound reflecting surface. Like you said , with careful placement and toe-in side reflections can be greatly reduced.
Good example would be a pair of Martin Logan speakers. They are dipoles and have radiation of about 30 degree horizontal and almost non vertical. Initially, someone may think that Martin Logans have to be easy to setup and are room friendly ( side reflections play very little factor with ML ). That someone could not be farther from the truth. In fact those speakers are difficult and tricky. However when setup is optimize they can be very rewarding ( got'em for 6 years ).

Also:
Using the mirror technique where you see the other speaker's tweeter on the side walls.
Where each speaker's tweeter bounces of the rear wall to your ears at listening position

See: http://www.realtraps.com/art_room-setup.htm)

I don't think this will answer all your questions, but the diagrams should answer some.

There's an Acoustic forum over at Audiocircle as I know you frequent there. There's several manufacturers that are very kind and helpful even if you don't buy their products.

Don't forget bass traps. Doing your room acoustics will create a major upgrade that most of us hadn't anticipated and wouldn't do without again.

Just don't over-treat your room.
It's a common mistake.
Start small with 1st reflection points,
then experiment with absorptive/diffusive or both kinds of materials to treat front wall.
Bass traps help with coloration of lover frequencies and will smooth-out a boomy bass in problematic rooms ( I use Echobusters phase 4 for their flexibility. One side is a diffuser and the other is absorber).
In my opinion this would be a good start.
Later you can try treating a back wall.
In my newly constructed room I have used a 1/4inch natural cork tiles to cover entire back wall & few shelves with books as a natural diffusers.
Treating a ceiling is another matter, but not many are willing to go the extra mile.
Email me if you have any specific questions.
I will try to help you if I can.
Good luck & happy listening.

I don't really have any corners to speak of, and since my room is large enough I've been told off-line by a knowledgable person that I don't have typical small-room bass issues, but I do have an 8' free standing wall about 3' behind my head I think I will address.
To this point, thank you all for your assistance. It really helps to hear from folks who've lived through these experiences.