Before fighting Venom, go to the upgrade menu and make sure you have the melee attack volley. Depending on your health level, you may or may not want to use the power up. At the right moment, jump over Venom, confuse him, and chip away at his health. Repeat until his black suit begins to "glow". Now, when you jump over him he will run away. Take this opportunity to use your new attack and chip at him, occasionally giving some hits. Keep hitting him until his "glow" gets stronger. Harry will eventually tell you to knock Venom into the air. He'll fall back to the ground confused, same as before. Repeat until his health is low and you can finish him off.
Use the following strategy to easily defeat Venom the first and second time you face. When you meet Venom at the construction site, you must beat him down in five minutes or else Mary Jane will die. The best way to do this is by defeating Venom in version one. Version two is slightly harder. Simply watch his five punch combo and the last punch, which is his super punch. After he is done with his combo, beat him up. Repeat until Venom turns into version three. Watch carefully and you should see a flashing symbol. Once you do, follow what the game instructs you to do and you should win.
The easiest way to defeat the second Venom is to jump around and fire adrenaline web. When his glow is high, go to the circle and press the selected button.