Parasitic elements at circuit level
how do we start looking into parasitic elements


This is something you learn by experience. 

Like, how to apply  Ohm's Law to life. ;)

We learn on the job, or from simulators like Saturn PCB.exe, that geometry is the key factor. 


For conductors that are straight, the inductance of a short wire with a length/width ratio, 
l/w = 6:1, L =  0.5 nH/mm = 5 nH/cm and 
l/w = 80 or 1.0 nH/mm = 10 nH/cm and 
for parastics we call it "effect series inductance" = ESL and for dielectrics they all have an "effective series resitance"= ESR
we discover that Murata makes low ESL RF SMD caps that l/w=1:2 instead of  2:1 ratio like 402's, 603's, 1206's


For Diodes some learn as I have that C_diode = k/Pd meaning the 0V bias capacitance increases with power rating from bulk size for some figure of merit k  
but material like SiC or Si or GaAs or Si- metalized terminals of Schottky diodes can reduce the internal series resistance , Rs
and for all diodes the Pd rating * Rs is somewhat constant in the same materials of different sizes meaning the incremental resistance reduces and junction capacitance rises with increasing diode sizes.


this is why CMOS ESD diodes can only handle 5mA DC yet are faster than the CMOS they are protecting from Latchup failures. if they were too slow, how could they protect CMOS?

you learn how to calibrate your fingers tips in pF with a 1mm gap or nF with pressure. 
you learn what is the capacitance of a trace over a ground plane by the geometry of trace width to dielectric thickness in pF/mm
the same is true for twisted pair being around 100pF/m with some standard dielectric thickness and that the twisted pair impedance is \$Z_o=\sqrt{ \dfrac{L}{C}}\$    
just as it is for parasitic PCB traces with ESL and C to ground plane to make a controlled impedance strip line.
this but increasing can increase thermal noise.

you learn how to deal with MOSFET Q charge and Ciss, Coss which occurs due to Vgs threshold crossing the Ohmic boundary and that Q*RdsOn is somewhat constant or is affected by design, quality and cost or Vds rating.