Jakiro is an amazing support that most people I've spoken to underestimate him greatly, all the more shock to them when you MVP the game helping/destroying them! Here is the whole guide in full 1080p but i'll also be adding it all in text here
His First ability in order of appearance, Dual Breath looks like two abilities in a cone area in front of Jakiro, it applies a movement and attack speed slow and also does alot of front end damage followed by a damage over time effect.
Use dual breath at the base of your character, in the direction you want to breathe, it will travel just as far as if you clicked behind your enemy, but if you clicked a little out of the range your character will move and THEN cast it. Uh-oh you MISSED!
His Second ability Ice Path is a rectancular line attack that deals no damage but stuns after a very small delay
When you are using Jakiro's second ability Ice Path try to freeze where your enemies are going to be, not where they are now, don't be put off by people on your team complaining that you missed an ice path, if you saved a teammate making the enemies hesitate that can be just as powerful as landing the ability
Your first choice when you get into the game is what spell to choose, we're choosing liquid Fire, which is a passive ability with no mana cost, its a small Damage over Time Area of Effect spell that slows your enemies attacks. it will push your lane a negligable amount but the extra harassment power is worth it
His ultimate Macropyre, is much like ice path in reach, but causes large amounts of damage over time to any enemies that stay inside the effected area, the spell itself does no upfront damage.This ability can be improved by the item 'Aghanim's Sceptre', which increases the cast range, distance, and the amount of flame strikes on the floor.
Using Ice path AND Dual Breath you can Crowd Control two targets, but try not to overlap them and use them together to keep people in Macropyre for longer.
Two of the basic situations are like this:
The opponent is a long ranged enemy / at a distance away from you, Since dual-breath is a pretty short range spell, you would have to cast Macropyre and then Ice path to hold them in place, but because you are not opening up with dual breath, the enemy will likely reach the borders of macropyre before ice path hits them due to not being slowed, and thus will receive a lot less damage.
The opponent is a melee enemy / close to you. This is an optimal position for this combo to work, because now you can dual-breath the enemy before casting Macropyre, and then drop ice path on him before he reaches the edge of the burning effect on the ground, allowing for full damage of the spell. Congratulations, your enemy has been burnt to a fine crisp and can be served with fries.
Once you run out of the starting consumables, you usually won't buy any more. If you are in the mid lane, you should get a rechargeable Bottle that also helps you take the runes, or if you are in a side lane, you should pick up a Ring of Health from the outpost or Secret Shop, which you later buiild into a Pipe of Insight.
After the Bottle / Ring of Health, save up 500 gold and purchase your Boots of Speed from either the outpost in the side lanes, or the main shop in your base and have your courier ferry the item out to you. Having this item can very easily mean the difference between life and death against a faster opponent.
The next part may take a while if you are in a difficult lane or laning with a partner, save 1000 gold and buy an Energy Booster, completing Arcane Boots. At this stage in the game a lot of your allies will only be able to deal massive damage with mana and now you can give it to them and they will love you for it!
Next start to complete your Mekansm by buying the Ring of Regen from the base or outpost for 350 gold, and the pattern for Headdress for 200 gold. With your new item you have even more lane staying power, and an area buff which heals teammates and minions that will give you a stronger pushing force when trying to take a tower.
After this save 550g and buy Chainmail from the outpost or base and the 200 gold pattern to finish Buckler, this works in a similar way to arcane boots but gives an armor buff instead of mana, your teammates won't celebrate you unfortunately as the visual effect doesn't really show, but you get to feel the satisfaction yourself when your team took alot less damage because of you.
At this point inbetween buying Observer Wards and finishing Mekansm for 900 gold the game may actually be over, don't worry if it isn't, but it is a possibility
With any accidental (or intended) kill gold you may have received, upgrade the courier to Flying Courier and buy wards, but don't just wait for a kill for these, try to weave them in all over the course of the game.
Do NOT jungle, if you are in the jungle you aren't doing your job of supporting. If you must be in the Jungle double stack creeps (For other teammates) and only take the easy creep pack for yourself but concentrating your attacks (and thus liquid fire!) on the creep with the biggest health. Use the money you do make towards a Ward : )
In a teamfight stun and slow as many people as you can! It sounds simple in practice, but in reality it's tougher than it sounds. Everything you can do has an area of effect element to it so make use of it!
On a similar note try to include as many people are you can in the buff areas for Arcane Boots, Buckler, Mekansm and Pipe of Insight.
If you have more stuns and slows on your team try not to overlap them!
For Arcane boots, Buckler, Mekansm, and Pipe of Insight you can ping yourself if you think that somebody could benefit from these buffs, but is moving away from you, or you could also mention the first couple of times you use it to "Gather at me for Arcane boots", and pray that people learn you have them.
Try to keep the merchant out of stock of Observer Wards, winning a public game is all about vision (but when isn't it!)
If you have more stuns and slows on your team try to be first to use Ice Path at long Range, as with your range no one can overlap your stun wasting the duration of other stuns that could be stacked one after the other. And be last to use Dual Breath at short range, the other public player with a slow will more than likely use his first leaving you to add on at the end with much better timing.