If your stopper is attached to the p-trap, removing it may cause water to leak. Be ready to duct tape it or have a towel or small bucket to catch the leak.

If your sink has a stopper plug, take it out.

This will give direct access to the clogged drain and improve suction.

Most sinks have detached stopper plugs. However, some sink stoppers are connected to the p-trap, so check which type you have and adjust accordingly.