stacking camps, you just need to make sure theyr outside of the spawn box at the end of the minute, so right click or draw agro at 53 seconds and run away, plenty of youtube videos for an exact representation, or just watch someone else do it.
if you dont want to random, you can try modes like Single Draft, gives you a choice of 3 heroes to play, so you have some choice atleast.
jungling, theres no real trick, some heroes are obviously better at it, but otherwise, just know your limits, manage your regen and try to keep yourself active on the map, ganging and pushing when necessary.
if you're looking to jungle, try doom out. he can devour creeps, gaining their spells or passives. his ulti is the scariest thing ever, silences you and mutes items. after that hes a normal fighting character, with a mediocre nuke and good sustain with his scorched earth or whatever its called.
lifestealer and natures prophet are also good in the jungle.
if you like assassin type heroes, riki, clinkz and bounty hunter all have windwalk.
Templar assassin with blink is great if you have good micro skills.
mage type heroes, leshrac is really popular atm, lina and zeus are always good choices if you're going for a mid or farming caster.
lion, disruptor or undying are good if you're looking to support.