When I play at local tournaments, I sometime see people laying down big hands which turn out to be a good fold. (If that was me making the decision, I would have called, and lost). I see people making very accurate reads of players hands and understanding how the board hits certain players range. - How do they do this.

I've tried to poker videos on youtube and twitch (Doug Polk, Neeme, Pokerstables etc) to see how they play different hands but I can never understand some of the decisions that they make despite them explaining it sometimes.

My BIGGEST issue I think, is defining opponents range based on their action during a hand and knowing how to play 'correctly' pre-flop e.g. 3/4 bet hands and post flop in different situations - when to check/bet/raise/fold properly. I don't even know how to bet to represent certain hands. I tend to play 'instinctively' which I think is what is causing me to be a losing player.

Please advise me on how and where I can improve and stop being a little fish.

Thanks in advance.

This is a pretty generic question, so here is the standard generic advice

1. Practice your reads when not in a hand. After you fold preflop, focus on a player in the hand and try to put togethe rthe information (what type of player is he, how has he been playing) with his specific actions to try and narrow the range. Use this to try and predict what he will do next, and also to predict the type of hand he has. Keep doing this all the time, and you will get better and better at reading ranges
2. Spend as much time working on your game off the table as on the table. Focus on specific things, and read on those topics, simulate hands with equity calculators, and make notes of things that you want to add to your game. When you play, play each session with a specific focus and goal. After each session, take notes, analyze interesting hands to see if you made the correct decison in real time
3. Post interesting hands here. Interesting hands are not hands where you are looking to validate a decision you made which resulted in a bad beat. Interesting hands are hands where you were faced with a difficult decision, and, regardless of how the hand turned out, you would like feedback on your decision making process. When posting hands, do not post the results. No one here actually cares how the hand turned out or what the villain held. We are interested in understanding you decision making process to see if we can help improve that.
4. I said it before, i will say it again, take notes, record any hands that you think you misplayed (and what state of mind caused you to misplay the hand), document any players that play a style that you want o emulate and try to understand how they play.

Improving at poker is a gradual and hopefully steady process, and works best if the game is studied with discipline.

SpewingIsMyMove had some great advice above^^^
As far as the third thing you mentioned about defining a players range based on their action and how to 'correctly' play preflop, I would take the time to memorize a general Raise First In Range for each position. This will mentally give you a solid foundation as far as what hands a player could have in their range from a given position. With that said, you can now adjust a players specific range from information you have gathered from their actions. If a player is super tight and RFI from early position, chances are a standard player might RFI 77+, AJs+ KQs etc while this nit might only open TT+,AQs+. For example, against this player on a 7-6-2 board, their range would have overpairs and overcards but rarely a set, two pair or a straight draw with a hand like 98 or 54 because they have shown you in the past they don't have these hands in their RFI from early position.
As far as playing 'preflop' correctly it's a matter of first learning what your Raise First In Range is from each position. After that you need to learn what your range will be facing a RFI and also what your range will be when you RFI and face a 3-Bet. Upswing poker has free preflop RFI charts you can get via email to start to understand what ranges are what from each position. Hit me back if you need more help. Hope this helps

You will most likely improve financially by not playing live tournaments.
your pretty much hoping to run hot. Luck is a huge factor in live tournaments.

This is something to consider. If you are playing for fun, liver MTT's, imo, are more fun. But if you are playing for profit, live MTT's can range from 'Maddeningly high variance' to 'You are better off playing bingo'.

When considering your strategy, you have to consider the player pool and tournament format. Low buy in, re-entry\rebuy tournaments with a structure designed to finish in 4 hours or less (a common format for local, daily tournaments) will attract a less sophisticated crowd, and require a less conservative strategy. It will therefore be higher variance. In this style of tournament, fold equity is lower, ranges are wider, and there is less opportunity (in the later stages) for multiple streets of post flop play, as it is typically shove or fold.

If you really play better poker, look for tournaments that are deep stack or monster stack (15k to 20k starting stacks, which usually is between 200 and 400 bb) and 30 minute levels. You want a tournament that usually takes over 8 hours to complete. This will give you more time to try more sophisticated strategies.

But just be ready to weather some maddening variance.

agree live mtts are sexy as fark.