In general, "more understandable" and "less Lines of Code" are mutually exclusive. Reducing lines of code frequently reduces readability, and thus understandability.
There is no magic formula we can give you to write good code. It's a combination of a readable, consistent style, with good design and documentation, and (in general) adherence to standards and Best Practice guidelines. It's experience that makes good code, not Key Points.
It is difficult to calculate execution time from a look at the source - certainly Lines of Code estimate will not help: a single line of code could look innocuous but take minutes to execute:
foreach (MyClass mc in list) mc.Save();
You can measure it though - look at the
Stopwatch class[
^]