XLink Viewer:
scroll through all spectra (files) and see if you find some monolinks with a good assignment (lots of colored (red/blue/green) annotations.

check Peptide Mass (err Da, ppm)-->  Compare calcPepMH, precursorMH.
--> check mass accuracy of the MS-run, it should be around +- 0.00 - 0.05 Da.
however, there will be outliers, most of them around the next bin i.e. -1.02 (C10_MSMS_2396...), especially at masses above ca 1700 Da caused by incorrect peak picking, but also simply off because of incorrect internal mass calibration

(it's therefore a good idea to add (at least) three internal standards to the matrix before spotting, i.e. two for automatic internal calibration (MH+= 1046 (Angio II) and 2465 (ACTH clip 18-37) in processing method) and one in between i.e. MH+ = 1296 (Angio I) or 1672.9 (Neurotensin), to be able to check later if automatic calibration was achieved successfully) otherwise manual re-calibration can be done later.

quickly check for looplinks as first hit candidates to confirm that there was successfull crosslinking going on in the protocol
"correct" fragment matching:

We've successfully matched only spectra with at least three matching b-or y-ion peaks.

Final results:
dependent on the mass accuracy observed accross the whole MS-experiment, we accept only such peptide candidates as being "correct" that have masses within the observed mas error for high-confidence mono-links. this is usually done in MS Excel by sorting all correct monolinks by mass error in ppm. Exception might be caused by incorrect peak picking (m/z of mono-isotopic vs. strongest peak) or incorrect mass calibration (peak intensity, m/z of mono-isotopic vs. strongest peak)

Score.
The score is an additive function of the number of matched fragment ions (b-, y-type ions, multiply fragmented precursor ions, ions derived from neutral losses of H2O (-18), NH3 (-17) CO2 (-44) to a theoretical MS/MS spectrum, immonium ions, reporter ions, 
monolinks are easier to be matched than looplinks and xlinks, generally in this order.
However, xlinks allow more theoretical fragments than mono- and looplinks.
therefore the "score" can be missleading. a mono-link might be 

there should be multiple matched peptide fragments, evenly distributed throughout the whole spectrum.
b- and y-ions are more likely to be observed than others.

Reporter Ion
the presence of a so-called "reporter ion" can indicate if an MS/MS spectrum is derived from cross-linked (same for loop-linked) or monolinked peptides.

i.e. we tend to observe a fragment ion at m/z=240 for DSS-or BS3 monolinked peptides. This is derived from a lysine immonium ion (84 Da) modified with DSS-OH (156 Da), this could previously be observed in about 50% of all correctly assigned monolink MS/MS spectra. used for scoring
Of course a non-lysine N-terminus modified with DSS-OH is not expected to show such anion 

also, we tend to see a "reporter ion" at 222 Da for DSS-/BS3-crosslinked peptides containing at least one lysine residue. 
(for details, see manuscript)
 

Check for an ion at m/z=175 that should be assigned to the Arg (R) y1-type ion from the C-terminus.

dominant fragments often contain a prolin (P) residue at the N-terminus. ergo, the P.... ion(s), if present, tend(s) to show the strongest signal in an MS/MS spectrum. 


in case of peptides containing singly oxidized methionines (M#) there is often a series of signals expected that are about 63-65 Da less than the predicted ones. i.e. look for signals at precursorMH -65 if there is a strong signal. That might indicate a correct assignment. That also could lead to a low score if most other fragment masses are 65 Da off the theoretical mass. doXLINK does not calculate fragment-65.


Reasons for a low score, but potentially correct precursor assignment:
"unfortunate" peptide termini
Stable peptide (during fragmentation) seem to contain basic residues at which a positive charge (a proton) can be stabilized. Therefore, peptides with an Arg- or Lys- C-terminus usually show good fragmentation and y-ion series. B-ion series are most likely found for peptides with a basic N-terminus. Peptides modified with Crosslinkers at lysines and N-termini are therefore expected to  show a poor fragmentation behavior, they don't show fragment ions that are evenly distributed throughout an MS/MS spectrum.
see i.e. monolink A14_MMS_1348....VVRFDK#LPGFG, no R- or K-C-term

there will in general be more assignments for larger peptides, since more theoretical fragments are expected, especially in the higher mass range of an MS/MS spectrum.