Baiting? What's that?: When I bait, I usually have a pre-made plan to ensure my escape with very low health and trying to land a kill while I'm at it or to just seperate a greedy carry from his team. It is risky sometimes and that is why I prefer characters with life saving juke/escape abilities.
Well how do you do it?: This applies for almost any champion, although the techniques you employ might differ, the strategy is the same. I will try to be detailed in my description and although it may take long to read, the planning in game must be quick.
*You WILL NOT be able to consider all of these factors accurately, but that is what makes baiting rewarding and risky*
Your Survivability: If you want to bait, make sure you are lightly outside their kill range or appear to be close to kill range to make them greedy and try to put you in kill range. You want to make sure you always have a trick to pull out of your hat encase they do something unexpected or your kill attempt fails. It is essential that you have a clear escape route because even if you just need to kite away from the minions and land the kill, the enemy team could always be in the bushes. Also, heavily consider your vulnerability to CC. CC could easily be the end of you.
*About the bolded statement: My Rammus build always makes it seem that I'm easily killable because I have low health and low regen. The big visible health bar makes it appear as low (compared to a tank) but most do not consider the 400 armor I can easily reach. With 400 armor, I take ~93% less physical damage, so they will usually think they can kill me and it allows baiting to be even easier. Even if they hit melee range or chase me through bushes as a ranged, I will still take about 20 damage a hit. This is usually long enough for my team to come and slaughter the chaser.
Your Team/Your Potential to Kill: When baiting for a kill, you need to make sure your team is behind you or that you can turn around and kill the champion once a cooldown comes up. Baiting is really frustrating in solo queue. Most of the time, your team might not know you want to bait, which is why I like Corki because I have solo kill potential. Anyway, if your team has ADD, you will need to communicate with them to hold position. Make sure if you bait more than one person, your team can handle it and escape safely after scoring the desired kills. When you're baiting to try to solo kill someone, make sure that if your kill attempt fails, that you can still escape. If you cannot escape after unleashing all of your power, you might die.
Their Team/Their Potential to Kill: When baiting, you have to consider the possibility of the other team appearing to help or if the other champion has a CC and/or burst potential. Always watch on the minimap before baiting to see if you catch a glimpse of a nearby enemy. They might be waiting for you! Warwick is a perfect example of nice AND dangerous bait. Low Health Warwicks usually get cocky when trying to get kills because some think they're invincible with Hungering Strike and Blood Scent and this sometimes work. Use this to your advantage, but also be cautious. Before you bait the Warwick, keep a safe distance for him not to Hungering Strike you. Try to bait the Warwick through a few bushes and then wait for him. If your kill potential is high enough you could kill him and get good gold. However, what if the Warwick has his ultimate? It is GG. Some people save heal, rally, summoner spells, and ultimates until they can turn the tide of a 1v1 which makes baiting very difficult. Which leads into my next point.
Enemy's Shock Factor: This is the most easily overlooked aspect and is sometimes impossible to track. Well if you can, try to keep a careful eye on the enemy's ultimate and summoner spell usage. If you can keep track and have a knowledge of the cooldown, you will know if that pesky Warwick will jump on you into Infinite Duress or if that silly Twitch will pop heal just as the killing blow auto attack is in mid air. This also applies to enemy skills shots and flash abilities. Will that Nasus's friend Kassadin teleport in and kill you. Will the enemy Blitzcrank hook you from the bushes to save his friend?
Your Shock Factor: This is what makes baiting usually successful. Make sure you can accurately calculate your ability's damage and general effect it has on the enemy. If you're baiting as Corki, make sure a surprise Phosphorus Bomb -> Gatling Gun combo will kill. As a Rammus, make sure to see your enemy's armor penetration and make sure you could survive about 5 hits to wait for your team. Overestimating and underestimating your shock potential can lead to your death and missed kills. This takes time, but the reward is so sweet as you kill someone with 40 HP left.
Well how do you do it?: I cannot answer that. Each character can bait in different ways. Rammus is good at long term baiting to set up an ambush. Corki would be good at turning around and unleashing the nuke from hell. I would have to write a long guide giving the details on how to bait with various champions. (and I only played a few X_X) This is just the basics to consider on almost every character. Some factos are easier to predict on some characters while some are hard to determine.