Jupiter and the moon, both bright and easy to spot, will been in the sky right beside Mercury on different evenings. That means you can find them first and use them to help you find Mercury. Mercury is at its best after about the 9th of May, when it starts appearing just above the western horizon right after dark. Find a place where the western horizon is free of obstructions and start looking around 9 pm. Jupiter is the brightest object in this part of the sky and should show up easily.
Mercury starts off to the right of Jupiter and much closer to the horizon.
By May 13th through 15th Mercury has brightened considerably and has pulled up beside Jupiter on the right. Binoculars can help you find it. Start with your binoculars on Jupiter and then pan right, ever so slightly, and Mercury should come into view. After the 15th Mercury will continue to rise higher above the horizon while Jupiter drops away. Mercury will also be growing dimmer, and will become harder to spot.