Take a careful look at enemy's stats before the fight, especially their move and attack ranges. Then what I usually do is that I calculate the distances and move all my troops to spots where they won't get attacked for round 1, and as enemies will move forward in round 1 and thus enter my attack range, almost all of my troops can then attack and probably finish couple enemy troops in round 2, so when the enemies are eventually able to hit me, they won't have much attack anyway and I'll thus suffer much less losses.
You'll probably need to enter the fight, move your troops around, surrender before the end of your first round to avoid any losses, and repeat this process for couple times to figure out the optimal solution, but it's definitely worth it. I'm currently fighting encounters 6 provinces away and I can finish almost all of them with losses less than two troops, sometimes even less than one. With the help of terrain, you can even finish a fight without any losses, especially when you are against treants and knights because you can kite them all the way till their death.
Here is another very useful post detailing battle strategies and things you need to know
https://beta.forum.elvenar.com/index.php?threads/encounters-guide.488/