Not looking at the preview
The message preview shows your tags in action. If you look at it and your \b{Bold text} isn't bold, you have made a mistake!

Using / instead of \ to start a tag
Don't get confused with standard HTML tagging:
/b{Bold text tag} is wrong,
\b{Bold text tag} is correct.

Using parenthesis instead of curly braces
\b(Bold text tag) is wrong,
\b{Bold text tag} is correct.

Using the wrong case in tags
\B{Bold text tag} is wrong (\B{ } is not defined),
\b{Bold text tag} is correct.

Not escaping commas where necessary
Advanced tags use the comma to separate the various arguments. If you need to use a comma and not have it treated as a delimiter, you must escape the comma.
See the discussion under "Special Characters" for further explanation and many examples.

Putting spaces where they do not belong
\ b{Bold text tag} is wrong (space between \ and b).
\b {Bold text tag} is wrong (space between b and {).
\b{Bold text tag} is correct.