Tricky spaces like that will just drive AF lenses crazy - a wire mesh at the front and also at the rear of the subject. So manual focus is very helpful in those situations, and you're off to a great start. Thanks for sharing.
Manual focus will naturally become instinct with time and practice. I was taught to - first compose, then look at the subject, then focus, then shoot. When the subject is focus-peaked, rotate the lens barrel a little bit further until it loses peaking... then go back the opposite direction to peak but keep going until it loses peaking again. By feel and without taking your eye off the subject, take a mental note of how much you rotated the lens barrel between extremes. Then rotate back half-way... and take the shot. Discipline yourself to do this only once, and trust your first instinct. Resist the temptation to repeat going back to those extremes to double-check.
Generally, if your subject is a 3 dimensional object (like a sphere or a cube) focus on the surface or corner or edge nearest you.
When you're taking a 'heads and shoulders' close-up of a person (or an animal), always focus on the catch-light of the eye closest to you. A catch-light is the tiny dot of light reflecting off the eyeball.
Have fun!
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