How to fix the "OCI not properly installed on this machine (NOE1/INIT)" error?

Q:

I get the "OCI not properly installed on this machine (NOE1/INIT)" error while connecting to Oracle database with FlySpeed SQL Query. I have Oracle client installed on my PC. How can I fix it?

A: 

FlySpeed SQL Query requires Oracle 32 or 64-bit client. (according to the bitness of FlySpeed SQL Query) Client Software to be installed on the workstation:

• Full Oracle Client installation. It requires the standard install procedure and contains both 32 and 64 bit driver versions. FlySpeed SQL Query uses the client that is installed in the primary Oracle_Home directory, if a different location is not specified explicitly in connection properties.
• Instant Oracle Client. To install it, download the Oracle Instant client archive (mind the bitness!), unpack it into a folder and add it to the PATH environment variable:
  When you are using TNS names, put the "tnsnames.ora" file into the same folder or use the TNS_ADMIN environment variable to specify location of this file. Also set the NLS_LANG environment variable to the required value (usually "English").