Well, the general rule for the syntax for lxEnvironment seems to be the following:
- the content of variable
expbefore is printed (results in \begin{) - the name of the environment, here
equation, is added. Now we have: \begin{equation - the content of variable
expafter is added, with 
 changed to a newline. - At last it seems that the cursor is set to the (first?) blank line or more simple after the closing
} of \begin{equation}.
The given complete code:
<lxEnvironment name="equation" parameters="1" desc="Math environment" icon="math.bmp" index="10" expafter="}

\label{eq:}
\end{equation}" expbefore="\begin{"/>
You can test this by changing the content of expbefore for example to expbefore="\begin{equation}

\label{eq:" and expafter to expafter="}
\end{equation}". Then you get equation inserted after ...eg: and the cursor stays at the beginning of the blank line. I think that is hardcoded in the code of TeXnicCenter. To get that changed please contact the support of TeXnicCenter, located on the homepage of TeXnicCenter
For an easy testing you can for example create an file mycommand.xls like this:
<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?> <lxCollection version="1" xmlns:txclxp="http://schemas.ToolsCenter.org/TeXnicCenter/LaTeXCommands.xsd"> <lxPackage name="username" path="" desc="My commands" > <lxEnvironment name="testerle" parameters="0" desc="Math environment" icon="math.bmp" index="10" expafter="}
\end{equation}" expbefore="\begin{equation}

\label{eq:"/> </lxPackage> </lxCollection> <!-- $Id$ --> <!-- $Log: username.xml,v $ First version 2016/09/26 21:00:00 username no message -->
and copy it to the system path where Windows installed your TeXnicCenter, for example C:\Program Files\TeXnicCenter\Packages (64bit version).
After a restart of TeXnicCenter (close all TeXnicCenter windows, open then a new one) you can test the now loaded new environment testerle (to avoid problems with the real needed and installed equation) ...
