Know your data, then experiment.
Figuring out the right wildcard to use can be tricky at times, and wildcards may not handle every situation. For example, if someone abbreviates the title "engineer" as "Eng.", then surrounding "engineer" with a wildcard, such as an asterisk, won't give you the results you need.
One of the keys to using wildcards effectively is knowing your data. If you need to, open your tables and do some exploring. If your database is too large to know in detail, you should at least know the type of data in each of your tables. Also, you can experiment with different combinations of wildcards to make sure you get the right results.
Don't worry about making mistakes. Using wildcards in select queries can't damage your underlying data.