If you receive it, then rejoice! You can easily look at their profile, see what they’re wearing (Dangerous or Shadowy leaning) and then wear the opposite gear and strike. Raw stats obviously matter, but for some reason, equipment modifiers affect the outcome more than raw stats. There might be some multiplier on the equipment bonuses, but I don’t know. Also, using dreams is a big boost as well, but make sure you’re choosing the one associated with the stat you plan on using. Also, I believe the higher your dream, the more benefit it brings.
All that being said, you have an advantage on the first round, and a SIGNIFICANT advantage on the third round thanks to dreams, so you have a much higher chance of winning while you’re on the receiving end.
When sending, you’re at a disadvantage. You should try to balance Dangerous and Shadowy gear equally, but you’ll most likely be at a disadvantage either way. At least this way you’ll have a lessened disadvantage compared to if you had +0 total equipment in one stat that they just so happen to choose. On the second round, you can do as stated above, choosing the opposite stat gear to what they wear, as well as using dreams. You’ll have a good chance to win this one. The third round, they’ll counterattack with their own dreams, so you’ll probably lose.
In conclusion, being on the receiving end means you can easily make yourself more likely to win the first round, and whoever wins the first round has a high chance to win overall, considering the advantages they get. That’s about everything you need to know about winning sparring bouts.
Also, I’ll dispel the myth here that the one with higher stats will win the round. It’s more accurate to say that pure RNG dice are tossed, then some bonuses from stats are added on top of that. Even with, say, 300 modified Dangerous, don’t expect yourself to win against someone with 150 modified Dangerous reliably.