Inevitable red eye effect: Red-eye is caused by a dehydration of the body from smoking marijuana. Notice how you never sweat, have a sticky mouth, and dry eyes when you're high on cannabis? Red eye is easily remedied with any relieve eye drops. Put a minimum of 1 and maximum of 3 in one eye at a time (I have seen excessive amounts of drops cause the problem to actually worsen) just after you got stoned and than 1 drop in each eye 10 minutes before you encounter your parents or anybody that could be suspicious of you smoking cannabis.
Dry mouth or throat Get yourself a bottle of mineral water and keep on drinking it while in stoned state. Keep the bottle with you and use often, DRINK A LOT OF WATER. Water alleviates cotton mouth, munchies, and red eyes. It truly is a godsend to the unprepared stoner. Drink a lot though, like 5 glasses. You'll be pissin later.
Stinking of cannabis smoke Stinking is highly unlikely because cannabis smoke smell disappears quite quick, so if somebody says to you that your are stinking with marijuana it may be due to recent suspicions or something, again, the smell dissipates very quickly off clothing and hair. However, the hands continue to stink long after someone smokes, because that is the part that has been digging through bags of weed, rolling joints/blunts, packing down into bowls, holding sticky, and the worst, the tar-laden blunt roach that stinks to the high heavens of herb oil (smell your next blunt roach, you'll understand if you somehow missed that one). Remedy this by a THOROUGH washing of the hands with soap and warm water, or if that's into available, just RUB your hands around in something smelly like chips. Eat some buffalo wings or something.
Breath smell Unlikely, cause the smell is gone from your breath in 5 minutes maximum. Take a breath mint if you wish.
Posture A lot of kids and even adults lose themselves as their are being talked to. They end up wavering. JUST STAND STILL! I always used to lean against something to support me.
Knowing through speech/behavior Train talking and being communicative with your friends when stoned, it's easy. If getting high makes you quiet, than just smile and keep eye contact.