Here's code that works well for my purposes and handles the missing values by eliminating observations with missing values.
sample := Flatten[ Import[paht\sample.xlsx", "xlsx", HeaderLines -> 1], 1] ;
Dimensions[sample]
TableForm[sample[[1 ;; 10]]]
missingdata[entry] := Not[MatchQ[entry, {_?NumberQ}]]
subsetdta = DeleteCases[sample, _?missingdata] ;
regdata = subsetdta[[All, {7, 20, 3, 4, 2}]];
data = regdata ;
lm = LinearModelFit[data, {x1, x2, x3, x4}, {x1, x2, x3, x4}]
Although part this was domain specific, a greater part is familiarity with the appropriate commands and functionality of mathematica. This is why I believe that a few mathematica examples similar to that above would be very helpful to users such as myself that identify the commands need in going from data importing through a multiple regression problem. Thanks for pointing me in the right direction.