Know your opp's cooldowns. If the enemy thresh has Q,W,E and R up and you try to go in, it'll end bad for you. If he just missed a hook that's a window for you and your support to try and engage.
You don't always need to be aggresive, tho. If you're playing lategame hypercarries (Kai'sa, Vayne, maybe Trist or Cait) then you are fine if you just play safe and keep up a good farm. One of the biggest problems in silver/gold elo is that people doesn't know that it's fine to walk out of your lane 0/1/1 if you are 50 cs ahead of your opponent and they just try to engage over and over, losing a lot of minions in the process of engaging and giving up potential free kills.
As a general rule of thumb, regardless of the lane matchup, never go for a fight if you can't tell if their jungler is standing on the nearest bush. No vision and you don't know where their jungler is? Stay away. (Unless you are already ahead enough to be able to pull the 2v3, in which case you are probably already carrying anyway). Also never go for a trade you are not sure you can win. If it's been a farm lane on early and you and their adc are both sitting on a bf sword and boots, then whoever makes the mistake to expose himself for a trade is the one who eats the supp's cc and goes down.
TLDR: If you need to ask why are you losing so many trades, you are doing too many trades. Stop trading that much.