Vi is far and away my favorite champ. Hopefully I can give you something to chew on.
Since I don't play ranked, I have no problem sharing my Vi strategy with everyone, and I'd say it's a rather good one.
- Runes/Masteries
Marks: 6x Armor Pen, 3x Attack Speed
Seals: 9x Flat Armor
Glyphs: 3x Magic Resist, 6x CDR
Quints: 3x Attack Damage
Since most people will have Armor runes by default, the Armor Pen reds are great for making your early ganks hurt. A little bit of Attack Speed will help you proc your W more often (which in turn gives you more Attack Speed to keep the punches coming), and a little bit of CDR will let you proc your passive more often.
For masteries, I take 21/9/0 for maximum gank damage.
- Skill Order
Never take a point in any skill at the very beginning of the game, because circumstances may dictate whether you start W or Q. If you're getting invaded, you'll want to take Q, but otherwise you should start W. So wait till about 1:45 or so before you take your first skill point, just in case you need your Q for fighting.
In normal scenarios (i.e. no invade or early teamfight), you should start with your first point in W, your second in E, and then max out your Q for mobility and ganks.
- Clear Path/Ganks
Assuming an uneventful beginning, I will always start at the "medium" camp in bot lane (i.e. Krugs on blue side, Gromp on red) to get the best leash possible. I'll burn Smite to get the stun/poison buff ASAP, then move on to the first "big" camp. From there, I make my way to the other side and take the other "big" buff camp, with Smite assistance. After clearing that 3rd camp, I'll have both the red and blue buffs and be in perfect position to gank top at level 3.
If the gank is successful, I'll usually have enough health to clear another camp or two before my first back. I get my jungle item (usually Stalker's Blade, sometimes Ranger's Trailblazer) and boots, and wards/pots with any leftover gold. I'll then work towards the Warrior enchantment, which gives you a heavy power spike in the early-mid game. After that, the Trinity Force will provide a second, even more noticeable power spike. Those two items are my go-to core. I'll often pick up a Hexdrinker/Maw before the Trinity Force if the enemy team is heavy AP, or Randuin's against heavy AD.
One thing to note about my particular build and strategy with Vi is that it's ENTIRELY contingent upon landing your Q's. This build will provide damage out the wazoo and have the enemy tripping over their feet to run away when they spot you heading into a lane, but ONLY if you're landing your Q's. If you're not consistent when it comes to connecting with skillshots, then I would suggest ignoring this build and focusing on a tankier build.