There is not much to say... Dazzle is great babysitter, very good in teams where teammates know how to use your presence properly. In pubs rarely played as it he should be played. I guess you all know what i am talking about.
I would love i can say that there is one universal item/skill build in dota (not just 4 dazzle, but 4 any hero) but i can not. Different situations, different opponents forces you to take different decisions.
...are very simple. Courier - if noone is willing to buy one, you buy courier(its your duty)! If other support player is buying one, buy wards.
In this phase you must be aware of how's it going for your carry and you on lane, and predict how it will be 'till mid game.Common items are boot, soul ring or urn, bracer( thats why you have a gauntlet) or headdress/basilius. Well, basilius is not that common, but if hero you're supporting has low armor do not hesitate to buy one. Also provides good pushing aura, if youre up to taking/damaging tower early. Soul ring or urn? Urn if you can see you're gonna get some kills on lane, soul ring if your carry is struggling to get some farm. Headdress is also an option, if your healing is just not enough, and you're preparing for early tower push.
Why no clarity? Well, you have some mana. You have a tango and salve. Tango and salve are not for you, thay are for your carry. Give it to him! After that you can start healing with your wave.
Team items, more - better. Arcanes, Meka, Drums even Vlads are nice to have during team fights. But also, you must feel what fitts best to your team. If not sure go Meka.
This items are speaking for 'em self... Just think what do you need to provide more power to your team.
You should be not reading this guide if youre not familiar with Dazzle's skills.
In early/laning phase your main goal is to keep your partner alive/healty and happy. Happy carry is carry with enough farm, so do not mess with it. Harass as much as possible, deny as much as possible, do not last hit at all... And thats it. Its easy right? "Yeah, but how i will get my items then?" Its easy also. When your partner is using salve/clarity - farm. When your partner is jungling - farm. When your partner is with you on lane - DO NOT FARM!
Best way to defend/heal your partner is when he is near enemy heroes. Amount of healing from wave is good for you and him, but amount of damage is just bad for opponents, so use it wisely. If you have a lot of mana, you can heal a creeps just to harass enemy, or when attacking the tower to make creeps tank more.
Grave is your trademark spell. It takes lot of practice to start using it in the best momment. You should watch HP bar of your partner on lane, or of all allied heroes during teamfights. If grave is not lvl4, always use it on carry in teamfights(because of cooldown). Those 2-3 more hits from carry can turn a whole match upside down. Also, if you and your partner are chasing a enemy, and partner needs to tower-dive to claim a kill, do not place a grave instantly, wait for best moment. Its very hard to determine perfect timing, but lower HP your partner is, grave is making more difference. Grave should be followed up with healing wave, so chances of suriviving chase/fight are huge.
In teamfights your use your ulti wisely. Do not focus just to get enemies in ulti's AOE, try to catch as much as possible allied heroes. Difference in armor is huge advantage during whole team fight. Because of casting range of ulti, you're not limited with positioning, and best place is to stay behind. Do not go too far, 'cause you can not reach all heroes with meka or pipe. After casting an ulti, try to place poison touch on their carry, and heal, heal,meka, heal,heal, replenish mana, heal, heal, heal your allies... Biggest impact in teamfights is in mid game, when your presence is burnng as hell your enemys. Difference in armor, huge healing and 1 proper save are difference between wining and loosing, so you MUST be there in every single fight.