Throughout the course of most games, you are put in certain situations where your hand gives you multiple ways to play against your opponent. These multiple options all have different outcomes for the rest of the game, due to the outs your opponents can have and/or the responsive cards your opponent may have for your plays. However if this applies for you, this means it also applies for your opponent as well. While I do believe there is always one correct play in any given situation, knowing how to find the correct play can be difficult at times. But one way to find the best play from all the others, is to access the situation and see if it's better to play more conservative then aggressive. Knowing the difference of when to play either conservative or aggressive is another big way to change the overall course/outcome of most games. Sometimes it can even help you win games that you thought you wouldn't have been able to win as well!
There are many different ways a person can play conservatively within a match. One way is by keeping the more powerful cards in your hand, and using your weaker cards to bait out your opponents backrow. This means that throughout the game, you force your opponent to waste their defensive resources so that your power plays have a more likely chance of going through. This also means that your opponent is throwing their own resources onto the field to beat your weaker cards, thus giving you a chance to simplify the game and create advantage by running over the monsters they committed to the field. A simplified example of this would be when playing the Fire Fist mirror, and summoning either [ccProd]Coach Soldier Wolfbark[/ccProd] or [ccProd]Brotherhood of the Fire Fist - Bear[/ccProd] into an open field while your opponent has backrow. Instead of summoning Wolfbark and making any XYZ, you can simply summon Bear and bait out a set backrow. You're able to gain advantage of it if the attack goes through, give your Wolfbark play a better chance of going through, or even wait for when they draw a power card such as Tenki/Wolfbark so that you have your own Wolfbark play to combat with. (You're also able to make a read on their backrow based upon if the attack went through or not as well.) Another way to play conservatively is by not using your defensive traps right away in the early stages of the game. You want to be able to receive full value from all your cards so that you're able to gain advantage over your opponent later in the game. This means to NOT [ccProd]Bottomless Trap Hole[/ccProd]/ [ccProd]Torrential Tribute[/ccProd]/[ccProd]Solemn Warning[/ccProd]/[ccProd]Dimensional Prison[/ccProd]/[ccProd]Mirror Force[/ccProd] the very first monster you see summoned or that attacks. An example of this would be my round 7 match in game 3 at YCS Atlanta. My opponent had a face-up [ccProd]Steelswarm Roach[/ccProd], face up [ccProd]Fire Formation - Tensu[/ccProd] and a set backrow with 2 cards in hand. He had just used his 2 summons to make the Steelswarm Roach last turn, so I can assume the cards in his hand are either 2 monsters/hand traps because if they were backrow he would've surely set them. I have a [ccProd]Dragon Shrine[/ccProd], [ccProd]Dark Hole[/ccProd], [ccProd]Hieratic Dragon of Tefnuit[/ccProd], [ccProd]Hieratic Dragon of Su[/ccProd] and a Torrential Tribute I had drawn for turn. Earlier through the match I had noticed that he always end phase MST'd whenever he had it no matter how many backrow I would have and it would always be the farthest to the left. Since I had enough Dragon Rulers, and I wouldn't have a play for the rest of the turn, I opted to set Dragon Shrine (To the left) and Torrential Tribute. My opponent then plays his end phase MST on my Dragon Shrine. For his turn he proceeds to Tensu summon Brotherhood Of The Fire - Fist Boar. Do you Torrential Tribute here? (You have more than enough life points.) If you do it would be a 3 for 1 since he committed 2 cards into making the Steelswarm Roach. However, I opted not to Torrential Tribute yet. Why? Because I have Dark Hole in my hand, so even if he were to not summon again this turn, I can Dark Hole next turn and keep my Torrential Tribute for his future plays. He then proceeds to normal summon Wolfbark which is where I Torrential Tribute and wipe his board, getting full value out of the card. Getting full value out of your cards is effective in winning games, but don't do it all the time as it can also cause you to lose games as well. Sometimes by playing too conservatively it can be bad as well no matter how good it actually sounds. (I'll get back to this a bit later.)
Just like there are ways you can play conservative, there are different ways to play aggressive as well. When people hear of aggressive play, a majority of the time they assume it's bad. They believe it's bad because they think it means to just always disregard any punishing backrow your opponent may have, and using their power cards right away even though it wasn't necessary. However, there are situations where playing aggressive is correct.A good time to play aggressive is by thinking steps ahead and predict/know where the game will lead to in later stages. Earlier I wrote multiple options that you have give different outcomes for the rest of the game, due to the outs your opponents can have and/or the responsive cards your opponent may have for your plays. In aggressive play there are times where you have to steal the game winning shot. This means that the best play you have for that turn is by going for the game, disregarding any certain traps your opponent can have for your plays, simply because you would have lost the game anyways on the following turn. An example of this could be with having a certain amount of life points. You know your opponent has Wolfbark in hand, but you've less than 800 life points and have no responsive trap cards for his Wolfbark next turn. You also see that he has 4 set backrow, there's no XYZ you can make to stop his play as well, and your hand isn't strong enough to go past through his 4 backrow. Are you planning to go for game even though he has 4 backrow? I would still go for game, simply because Gagaga Cowboy is game no matter what next turn. Now lets say you didn't go for game and just decided to be conservative instead because he has 4 backrow. You weren't going to win that game regardless because of Cowboy, which is why at that time being conservative was actually bad. By attempting to go for game at that situation, you give yourself a better chance of winning that game you wouldn't have won. But obviously there aren't always going to be clear cut situations where you know your opponent will have game on the next turn. Let's assume your opponent didn't have any cards in their hand and nothing else would be an out to the situation except Wolfbark/Tenki. Would you still go for game? In that situation, I would first check to see how many Wolfbarks/Tenkis my opponent has gone through in that game. After I check through how many outs he has left in his deck, I would then check for what responsive traps my opponent has already played. The reason why I would check for how many Wolfbarks/Tenkis in my opponents grave is because if they have a low amount of these cards left in their deck, this obviously means that they have a lower percentage of drawing that out. If they have a lower chance of drawing that out, I don't loose yet, so I have turns to draw into my defensive cards/combo cards to get past their backrow. The reason why I would check for what responsive cards my opponent played is because that way I would be able to weigh the pros and cons of going for game that turn. A simplified example of this would be if my opponent has 4 backrow (Game 1), but I see that Torrential Tribute and 2 Mirror Force are both gone. At this point in the game, I shouldn't be worried to summon/attack with multiple monsters for game because those punishing cards can no longer be played. The best case is you will have game so that you don't give your opponent a chance to win the game. The worst case would be your opponent will have a 1 for 1 trade off with whatever play you have instead of having a punishing cards that destroys multiple monsters, and still not having a chance to win the game until they draw that out. But the worst case isn't bad at all because you were able to bait out their backrow 1 turn earlier, allow your following plays have a more likely chance of going through, and giving them 1 turn less to draw into what they need.
In Conclusion, there are many different ways to play both conservatively and aggressively. This is why it's very important to understand the difference between conservative and aggressive play, while also understanding the basic concept on how to switch from playing conservative and aggressive.