Probably the best advice that I can give you for meth, or any other very rush-based drug (cocaine, amphetamine, MDPV, crack, heroin, hell even methylphenidate) is- Don't chase the high!.
Meth is a very long acting drug- there is a lot of controversy about exactly how long it lasts, some people say 4-8 hours others talk about it lasting 12-18 hours PLUS. I think a lot of this comes from confusion about the nature of the effects- the rush (smoked/IV, I didn't get much of a rush from snorting) never lasted more than an hour and the primary noticible 'drug' effects (mood lift, desire to socialise, confidence, talkativeness, energy/strength etc) were pretty much gone after 8 hours, but I flat out could not sleep for 24 hours without taking seroqel or a LOT of benzos. This is why I don't take meth (or stimulants in general) that often.
This means that the meth is still effecting my body AND my mind for atleast 24 hours, so you when you are SOBER you need to decide on how much you are going to take, how you are going to take it (for instance, how many bowls you'll give yourself so you don't just keep puffing all night) and when you are going to sleep and make a plan before you start tweaking. Don't try to put off the comedown by taking more- you'll just make the inevitable crash worse. Don't compulsively redose- try not to sit around for prolonged periods of time repeatedly taking meth, this is the best way to ensure that your comedown is fucking hellish. Don't buy large amounts, don't have any sitting in your top draw- it won't stay there for long.
I've found that I have enjoyed meth most when I made the decision to take some in advance (generally to go to a punk gig on), I'd buy only what I'd use that night (a point) and I would inject half at home, go to the bar a bit after door opening, snort the other half with a mate (just a little top-up) before the bands started and when I got home again at about 5am I'd be coming down proper so I'd take 75mg of seroquel and be asleep in about an hour and a half. None of this sitting around for hours smoking a gram of meth in a night or having a booster shot every 20 minutes, let alone any of this 'I smoked some meth and long story short I stayed awake for 12 days because I because a satanic dog told me that I would die if I ever went to sleep' business.
Don't chase the high, don't chase the rush. In some ways that is the advantage of IV- you shoot it and it's gone, then you put your drug shit away, put on a t-shirt and head out that door- you gotta get to that bar promptly so that you'll already be there when that chick who you've had eyes on for a while turns up. But the idea is still a good one- get it, do it, go and do shit that has nothing to do with taking/getting meth when you're on meth, when you feel yourself crashing take sedatives if possible and sleep.
Oh, and spending ages in anything that is open 24hours at 3.40am is not itself suspicious- there are a lot of people who are out and about in the early hours, cleaners, delivery men, truckers, shift workers, taxi drivers...but you aren't any of these people and they all will probably recognise you as a tweaker in a way that people who work during the day wouldn't- most graveyard staff are pretty onto meth heads and their bullshit.