It is NOT NECESSARY to initiate teamfights in lane, try not to unless you are 100% sure that you could beat the enemy. You will be fairly weak in the early game so try to avoid any disadvantages. Farms up quickly from lane > jungle > repeat until you have your core items.
But of course, help your team whenever they are in trouble! Avoid roaming and ganking as Freya, it is not worth the time spent. Only ganks/roam whenever you have nothing to do, for example, you have done clearing your lane minions and jungle monsters. You can try to go to your nearest allies and help them out with their laning, if possible try to get some kills.
Mid Game
As the game goes to mid-game, start helping your team. Do not farm gold in a lonely lane and get caught by the enemy team. Look at the map every few seconds(Not just mid-game but the entire game!). If the enemies are missing from the map and you are far too deep in their side of the base, you should be careful. Take objectives such as Turtles, Lord and turrets.
Late Game
Every move in late game is crucial. A mistake could lead to a horrible defeat. Do not get caught. Initiating a perfect teamfight is the key to victory. Stick together with your team, do not simply jump in with Wings of Faith if your team is fall behind or out of positioning, it would be Wings of Death, R.I.P. If your team have heavy CC such as Tigreal, Alice, Rafaela, etc. You can follow-up with their ultimates and get a clean ace. Otherwise, you can try Wings of Faith into their backline(mages and marksmen) to try take them down in a few deadly critical strikes.
Weaknesses
Freya can get countered easily by Natalia which is a bad thing
Karina could be a pain in the … too!
And of course, heavy crowd controls could stop you.

But of course, help your team whenever they are in trouble! Avoid roaming and ganking as Freya, it is not worth the time spent. Only ganks/roam whenever you have nothing to do, for example, you have done clearing your lane minions and jungle monsters. You can try to go to your nearest allies and help them out with their laning, if possible try to get some kills.
Mid Game
As the game goes to mid-game, start helping your team. Do not farm gold in a lonely lane and get caught by the enemy team. Look at the map every few seconds(Not just mid-game but the entire game!). If the enemies are missing from the map and you are far too deep in their side of the base, you should be careful. Take objectives such as Turtles, Lord and turrets.
Late Game
Every move in late game is crucial. A mistake could lead to a horrible defeat. Do not get caught. Initiating a perfect teamfight is the key to victory. Stick together with your team, do not simply jump in with Wings of Faith if your team is fall behind or out of positioning, it would be Wings of Death, R.I.P. If your team have heavy CC such as Tigreal, Alice, Rafaela, etc. You can follow-up with their ultimates and get a clean ace. Otherwise, you can try Wings of Faith into their backline(mages and marksmen) to try take them down in a few deadly critical strikes.

Weaknesses
Freya can get countered easily by Natalia which is a bad thing
Karina could be a pain in the … too!
And of course, heavy crowd controls could stop you.