Original post is here: eklausmeier.goip.de
Most common usage of rsync is
rsync -anv ./ user@remote:/dir/
But when the timestamps of the files on source and target vary wildly it is better to use:
rsync -crntlv ./ user@remote:/dir/
The option -c stands for checksum. The option -n is used to not overwrite anything (dry run). Drop -n to actually run the command.
Option -t to preserve modification times, -r to recursively scan subdirectories, -l for symbolic links, -v for verbose output.
I don't use -p to preserve permissions, but rather let the target system decide how to create files, and leave previous permissions intact.