Does an IWB with shirt tucked in really work well?
Generally - no. It depends on your situation; concealment is obviously compromised when any part of the holster rests outside of your clothing, absent a concealing garment. If you are outside walking the dog, with holster in the front, positioned on the strong side, partly concealed under a short jacket (leash in your weak hand, naturally) - that can work. In full public view, you must maintain concealment, which dictates either an untucked shirt or a jacket, or both.
At night, I use an exterior leather holster with a thumb break, and also, a full-sized pistol (1911 .45ACP or police model 9mm with 4" barrel) as opposed to a J-frame revolver or compact semi-auto. In public at night, I use either a cross-draw shoulder rig under a jacket or an exterior holster under a 3/4 length jacket.
Aside from that, the best advice I can give you is to practice, practice, practice. And by that I not only mean range time: drawing, index calculation (range to target) and firing stance but situational awareness and intelligent (not emotional) threat assessment. Think through potential defensive situations in advance. Never forget that if you use a gun in self-defense, you will be made to account for your decision and that bullets cannot be recalled.
Freedom is always coupled with responsibility. Please take it seriously.