Lane Properly:
Talon is very good at farming. Level up his rake(W) as fast as possible to 5. This can essentially one shot a minion wave. Many people at lower levels do not understand the importances of balancing harassing with farming. Farm up well early game, dominate late game.
If Talon is laning with a partner, choose a partner with good crowd control. Talon can easily harass with his rake while still farming. Just use it while the enemy is standing by the minions you are trying to kill. When an enemy is low enough, get the partner to stun or snare and you can cutthroat in and use to burst to bring down the enemy. Note that cutthroat will not only increase your damage but silence the enemy so that they cant ghost/flash or use one of their spells to escape before you kill them.
If talon is laning top solo, once again focus on leveling up rake and farming with it. But with talon being alone he can harass more aggressively by using cutthroat to silence the target, use your skills and run away before the silence ends. This usually results in you dealing a lot of damage to the enemy than they can retaliate with.
When to engage:
I assume you mean in a teamfight. There are two ways to play talon in teamfights. The first way is to play like a normal assassin and stay behind your team hidden. Only when the team's initiator(tank/offtank) go in and the fight has started so you go in and focus their ap carry. I say this because talon has a silence which will prevent their ap carry from doing any damage.
Another way to play him that most people are usually reluctant to do is be the initiator. This will work really well if the opposing team does not have too many stuns and/or do not have oracles. You basically cutthroat into their ap carry and immediately ult to stealth. This will cause them to immediately switch to another target(preferably your tank/bruiser who has come in by now). A benefit of this is, you get to damage everyone with the beginning of your ult AND the end of your ult.
Build:
Talon is as I've said before a burst assassin. He bursts and then runs off. So if anyone ever tells you to built attack speed on him. DON'T. Build pure AD and armor pen on him. You shouldn't have to stay and autoattack because any tanky AD DPS can kill you in a toe to toe fight
I would start with dorians blade first. At first recall, hopefully enough gold to buy a pair of boots and the brutalizer. Next built the boot into Ionian Boots for the CDR (Once again berserkers's attack speed is less desirable compared to CDR where you can burst more often), and start of the blood thirster. Then i would finish the brutalizer into Youmuu's GhostBlase and bloodthirster. Afterwards i would built last whisper (that 40% armor pen is OP!) Infinity Edge and Another Blood Thirster to finish.
Runes:
When runing a champions there are two things to keep in mind. Do you normally have trouble early game and would like a early game advantage or do you do well early game and want to have runes that scale really well into late game.
If you do not do very well early game and need all the advantage you need, then build flat AD Marks. But if you do well and want runes to scale better late game, built Armor Penetration Marks.
For Seals, I would take flat mana regen(replenishment) because talon is pretty mana starved early game if he wants to farm well and still harass.
For glyphs i would take flat cool down reduction.
And for Quintessances, i would take Armour Pen.
Masteries:
With the new change to the mastery trees, assassins like Talon can rejoice! I won't tell you exactly which to put points into but focus on the offensive tree for assassin champions like talon who focuses on burst.
Summoner Spells:
The two I would recommend is: Ignite and Flash. Flash is of course one of the most powerful summoner spells there is. This can be used both offensively and defensively. If the enemy is just out of reach of your cutthroat and you can't jump to them for the finishing blow, flash will close the gap between you. Or defensively you can use it to create a greater gap between you and your enemy OR flash over a wall. You do not understand how many times that has saved my life.
Ignite's DOT and his Q's DOT does a surprising lot of combined damage. In addition ignite will reduce the amount of healing the opponent have/gets. So if you are laning against someone with heal or a lot of life steal, ignite will make you laugh gleefully as they die because they can't heal themselves from your burst.
In general, I would say it is an absolutely horrible idea to not have smite.
Smite allows you to clear the early jungle faster, but its more important aspect is control over Dragon and Baron. Most junglers will keep smite up as much as possible in the late game for Baron and Dragon so they have the ability to steal or take the objective more easily.
A stolen Baron or Dragon can easily help sway a game in a team's favor. The global gold (and buff in the case of Baron) is a huge boon to a team. It can allow you to stay in game if you are behind or seal the deal if you are ahead. By not running smite you are putting that at risk.
You might be able to get away with no smite if the enemy also lacked it, but you are making the taking of Dragon and Baron that much more of a gamble. If your team has smite and the enemy does not, then it is infinitely easier to steal both those objectives.
Nunu is one of the few junglers that could run without smite. His consume does comparable true damage to neutral creeps allowing for a lot more objective control compared to junglers without smite. Cho'Gath has a similar ability with his ultimate Feast, since it does such a large amount of true damage to neutral monsters.
However I'd still run Smite, it is just that important.
Update:
With Season 3¹²³, Riot has moved the jungle closer to its season one state wherein the monsters are much stronger. To compensate they have included some jungle only items (Hunter's Machete, Spirit Stone, etc) but overall the difficulty has been ramped up. This makes smite much more important for no/low sustain junglers. Without using smite you have to suffer much more damage from the larger camps, forcing you to fall behind as you retreat to the fountain to heal.
Best Answer
You want to make sure your teammates know what you are planning and are also in a good position to follow up when you get initiated.
I think baiting your opponents with Sona is very risky as her ultimate and abilities are very helpful to the team and she is incredibly squishy so she could be killed before your team could engage and punish the enemy team. I think it would instead be better to use a more tanky champion that can also hold them in-place or stun them (Rammus and Jarvan), or a champion that has escapes/can disengage (Akali and Kassadin).
As to how to bait the enemy team into falling for the trap, that is very tricky. You need to make the other team think that you are alone. One way of doing this would be for the bait to stand in an enemy team's ward while their allies don't stand in visibility of the ward.
If for whatever reason the enemy team looks too strong or you don't think you can take them in the fight let the person being the bait die and disengage. It is much better to only have 1 person die than the entire team.
There are also some Champions that have abilities relating to death that can enhance your plays, here are some examples:
Karthus: He can cast spells for 7 seconds after being killed thanks to his Death Defied passive.
Kayle: Her ultimate makes a champion immune to damage (2/2.5/3 seconds)
Kog'Maw: Moves faster and blows up after 4 seconds dealing 100 + (24 x lvl) true damage. During the early mor middle game where Kog'Maw isn't fed, it might not be a bad idea to bait with him, but once he starts getting to late game I don't think it would be a good idea to bait him.