I assume you use a bow, if so hunt everything. If you are a thief arrows are a good item to pickpocket from guards as well. Any of my stealth characters practice illusion for muffle and eventually invisibility.
In Skyrim I never really went with the Illusion route - stealth is powerful enough as it is once you level it up. That and knowing when you're hidden... (compared to Morrowind when I would murder my own mother to buy a ring of 100% chameleon ASAP). Always stay in stealth, you'll get used to that being your 'normal' speed soon enough, and the skill will start leveling on its own.
Other than that, alchemy is an awesome skill. Tons of good potions for situational use, and sell all the rest. Alchemy and speech level each other up that way. No need to even 'cheat' the alchemy properties if you don't want to, just buy out every alchemist shop you pass, eat the ingredients and take the experimenter perks, then turn it legendary and reallocate them once you hit 100 (make sure you know most of them first). No alchemist in Tamriel has any excuse to be poor.
My personal favorite enchantment for my bow is paralysis. I let my companions dish out the damage if my opponents live. Right now that's about all I can do since my graphic card is nearing its end of life and loves to drop me into slideshow FPS at random intervals (not always, but often during combat).
Pick one town where you want to sell all your stuff - Riften is good since the thieves' guild is there. Other than that, no one in Skyrim really needs to stay alive [the game will make sure you don't kill anyone 'important'], just remember to always kill the last witness so you don't accrue massive bounties. Steal everything that's not nailed down. If you're careful, you can do it without killing anyone if you want to play the Robin Hood type.
There is some decent info on stealth in Skyrim's help menu (accessed through the main menu I think). Fastest way to level is find a Nordic crypt and sneak up on the draugre while they're sleeping and stealth kill them with a dagger. Especially effective once you get the 15x stealth damage with a dagger perk.
When setting up a sniper attack vs multiple dispersed foes, use the maximum effective range your skill and obstacles will allow and target the farthest foe. Upon impact of your lethal arrow, your target's foes will pretty reliably converge on the body to investigate. This is the time for you to melt back into distance and shadow. And be patient as their investigation progresses to searching, then giving up. That is the time be carefully moving into position for your next target.
One variation is that if you are fairly quick and there are only two foes, you can exploit one foe's pause to investigate his dead pal by nailing him right then. If you miss however, be prepared for him to realize your location and come after you. That is, you can often fire one arrow into a sniper situation and maintain your stealth. Firing a second shot into the same hot area while foes are still on high alert will generally compromise your location.
If you want to level sneak really quickly and don't mind using a bit of an exploit you can use this method:
https://www.youtube.com/watch?v=LhNo0C-zoOw
Just make sure they don't see you. Getting attacked by a Greybeard svcks. :/
For a bow, I recommend either Zephry or Auriel's Bow from the Dawnguard DLC. Their base damage is weaker than the high tier stuff like Daedric and Dragonbone but they both draw about 30% faster than any other bows and this stacks with the Quick Draw perk. It runs out of charges pretty quickly but Ariel's bow also sets the target on fire for 20 damage and undead targets take triple damage. And it looks pretty.