Since no one else has mentioned this, assuming you have a effects loop on your amp, the placement of effects before and after preamp matter, so here is my mods to the General rule of thumb list:
>Pitch-based effects like harmonizers
>Wah and filter effects
>Modulation effects (chorus, flanger, phaser etc)
>compressor or limiter
<<<<Effect SEND
>Noise gate
>>>>Effect RETURN
>>>>>Amp reverb

EQs and Volume pedals can happen ANYWHERE (watch that the type of volume pedal is correct though)

Back to the OP questions:
Of course I can pick what I like, but want to know chain order(s) others
like to use and why. For instance, do you like:
1) the Tremolo before or after Delay/Echo? (Doesn't matter, question yourself if you turn on Tremolo and Delay at the same time)
2) Octave Up or Down before or after Distortion MXR M-115? Pitch should be the first thing after the guitar, period, so yes before
3) EQ before or after Boost/Overdrive? Again, EQ is applicable ANYWHERE. Remember the old rule of thumb, that EQ is the BEST WAY TO RUIN YOUR TONE (unless you use it lightly and carefully

That said, although I have a killer MFX box, and in the past had nearly every kind of stompbox available, I have to say I am in a purist cycle of just digging plugging my guitar into a tube amp and getting distortion and reverb there. And maybe a delay box in the efx loop. The rest of the effects are just tone suckers.

But there are no absolutes!!!! Play with it .