The first thing to know about playing Kagura is you should almost always take Mid lane with her. At the beginning of the match buy 1 Mana Necklace first, then prioritize Jungle Knight.
By the time you clear the first wave of minions, you'll have enough gold to buy the Jungle Knife. The next step after this is to take the buff from the jungle.
But keep in mind that if there are minions clashing at the middle of your land you should prioritize it more than jungle monsters. So once you've cleared minion waves and gotten your buff you'll be back to dealing with minions and pushing toward the first tower.
When you push towers you'll eventually get into fights with other heroes. When involved in team fights, always position your umbrella near enemies away from you so you can easily hit them and zone them out.
You should also time using your ult after your skill 1 hits an enemy. Not every time but it's a good combo to get used to using.
Kagura is good for helping out in team fights. Definitely, prioritize helping out other lanes if they get overwhelmed with minions or enemy heroes.