It was mostly self taught tactics mixed with a lot boxing and MMA.
One of the most important things is to keep your distance, balance and breath properly to use your full strength. Never fight if you have fear.
Body stance is quite important as well
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The moment the opponent goes for a punch dodge then grab him with an armlock, break his arm with your elbow then hit him in weak spots like his eyes or solar plexus. Otherwise catch his punch before it gains enough momentum then hit him or just dodge/block it till he runs out of stamina. Headbutts and kicks/knees also help in close range. If he chokes you don't lose composture and hit him hard in the face or arms. Be a raging beast. Analyze your opponent and his strengths and weaknesses.
A tall dude has strength and range, but most likely has poor balance and coordination. What's best in that case is to wait and attack his legs or lower torso, never the face. Making him lose balance is key. Use their own strength against them. Same with fat/overweight guys, you prolly can't beat them directly but they still have weak spots like the eyes or balls, they also lack speed and stamina so you can beat them in a fight of attrition.
Also try to never hit just one spot if your opponent defends himself, hit multiple places at the same time with no rest. Use your surroundings, they can help a lot if you are physically weak. Also don't overthink mid fight, follow your fighting instincts and determination.
All of this considering you already have decent training and good reaction times, for the latter I enhanced mine through practising ping pong and being a goalkeeper/playing fighting vydiah. Now I'm able to hit flies in mid air if I concentrate enough.
Now, if you ever faced a strong enough dude/professional fighter you're done for.
