I always found brewing the more mundane potions, like the ones used in the Hospital Wing, to be almost like meditation. Though that was largely because I had brewed them so many times that I knew the rhythm by heart.
The Priori incantatem is only useful if you catch your suspect quickly. If they have time to cast a number of spells it muddies the waters considerably. Veritaserum can also be beaten by a disciplined mind. Or by sufficiently devious one. Most do, yes. St Mungos has experimented with intravenous administration of potions but most patients and their families are very resistant to the use of 'Muggle methods'. Not just the purists either. Most wholly magical families, even halfblood families, have minimal contact with the Muggle world so they have little knowledge of Muggle medical methods. And there are spells that can get a potion down a patients throat even if they aren't conscious.
People make attempts from time to time, particularly with the television, but as I never had much interest in it, I have no idea whether they ever met with success. The Ministry generally frowns on it in case such things get out into Muggle populace accidentally.
I have found that it has to be a memory at a point after I have read the book and it has to be a memory that allows me to stay in the room. If I leave the room in the memory, I must follow in actuality. I can't remain behind. It also depends on what else I was doing while reading the book. The mind remembers more than we can generally recall but if I was distracted while reading the book then I can expect to find gaps in the text when I review it in the memory.
People are also predictable, something I have found advantageous on more than one occasion.