Question 1 -- What are the most common mistakes you see in new scouts??
I glossed over it in my guide, but overextending is the biggest issue that I see in scouts at the low or low/mid level. Overextending occurs when a scout has inappropriately pushed past the area where his team is located and finds himself stranded with no support (resulting in death). Typical scouts at this level are still learning about the meta game and don't know much about what the combo is trying to do or what the other players are doing. As a result, they end up pushing without their team through the flank and die for no reason. I attribute this to one of three different things:
-Not knowing who has uber advantage
-Not knowing push timings
-Lack of patience
Let's go over each of these.
Who has (significant) uber advantage?
Your team is always in 1 of 3 modes: pushing, holding, or backing up.
Uber advantage in favor of your team will allow your team to push.
Uber advantage in favor of the enemy team will force your team to back up.
If a team has uber advantage but is unable to push through to the next area, they will hold until they get uber.
Even uber (both teams having the same amount of ubercharge) is a grey area, and whether or not a team pushes or backs up is based on man advantage (who has more people alive at a given time).
It is critical that you know who has uber advantage so you know if you should be getting ready to push, back up, or hold. Your medic should be keeping track, so if you need to you should ask him (if he doesn't know he's not doing his job correctly). Once you know who has uber advantage you can act accordingly. It is EXTREMELY IMPORTANT that you don't push without your team or you will be overextending and most likely die. If you die, your team cannot push, and you are hurting your team.
It is very important you don't needlessly die when your team is about to make a major push. This happens when you push in too early before the rest of your team is ready and there with you, or when you push too late and the rest of your team is badly hurt. You need to coordinate with the rest of your team to make effective pushes.
Lack of patience
Some players get a little antsy and just can't stand still as a scout. They constantly feel the need to move around and think that they are "doing something". They fail to realize that holding is an essential part of the game. When holding, your job is to simply get buffed and prevent people from getting behind you while your team builds uber. THAT'S IT. No flanking, no excess scouting, NO NONSENSE THAT WILL GET YOU KILLED. Your job is to STAY ALIVE and if you're not patient, you'll run off and die. This will allow the enemy team to push or will effectively kill any push your team was trying to make. To learn effective holding positions, watch demos of other scouts. Question 2 -- How do I effectively manage my health?
One of the most important scout skills is buffing frequently, but that falls under the larger umbrella of health management. Let's start by considering the medic's perspective.
The medic class is quite possibly the hardest in the game; he has to keep track of a lot of things from uber advantage to positioning. The medic's objective, on top of all of the other things, is to keep everyone at maximum health (150%). This is of course wishful thinking, so medics must prioritize which people they will heal first. At the lower levels, a general medic heal order is Scouts > Roamer > Demoman > Pocket. The reason the scouts are at the top of the heal order is because they have such low health that they need to be constantly healed up to maximum health so that they don't die (other classes can take more of a beating before needing health). In addition, many times the scouts spend a lot of time away from the medic, so healing them first allows them to resume their post at the flank. A good medic realizes that if he is going to bother taking the time to heal a scout, he will heal him fully to 185 so that the scout can spend more time away from the medic. A medic's job is to follow his pocket around for protection, and let the other players come to him for health.
Now that we understand more about the medic, we need to also learn about medigun mechanics. If a person has taken damage within the last 10 seconds, he receives the normal healing rate from the medic of 24 health per second. However, if a player has not taken damage in the last 10 seconds, he receives "Crit Heals" which ramps up linearly over time. If a player has not taken damage in the last 12.5 seconds, he receives health from the medic at 48 health per second. If a player hasn't been hurt for 15 seconds, the player receives the maximum crit heal at a whopping rate of 72 health per second. Thus, the medic's heal order becomes significantly more complicated as he must determine which of his targets will receive crit heals for maximum efficiency.
How does this apply to a Scout's health management?
Crit heals are essential when it comes to buffing scouts. If you have taken damage within the last 10 seconds, it can take up to 7.5 seconds to fully heal a scout to 185. On the other hand, if you receive the maximum healing rate it will take less than 2 seconds. As you know, medics want to spend the majority of their time healing the heavier classes, so getting crit heals is the most important thing you can do in the medic's eyes. You need to realize that if you aren't receiving crit heals, the medic has less incentive to heal you, and in turn you will be "waiting around" for your medic to finally get around to healing you.
My general rules for health management for beginning scouts:
Whenever possible, avoid taking damage. It may sound obvious, but the more damage you are taking, the more pressure you are putting on your team's medic to accomplish his objective (keep everyone at 150%). This should not be a problem with the scout's speed and agility. The most annoying thing a scout can do for a medic is to get buffed to 185 and then immediately run in and get hurt, coming back to the medic for more heals. Let the heavier classes on your team take damage while you use creative angles and flanks to damage your enemy while they are distracted.
Seek out your medic for a buff if you have 125 health or more. Try to minimize the amount of time you are wandering around the map without a buff (see Guide Section III for reasons why). However, this does not mean that you should constantly follow your team's medic around or bother him every 3 seconds for a buff (for reasons I previously mentioned). Get a buff, and then move on.
Seek out your medic for a buff especially when your team is in the "holding" mode. Usually you can work with your scout partner to trade off holding the flank to get a buff. This way a buffed scout is always holding the flank.
Try not to get heals from your medic unless you have at least 110 health OR crit heals. You don't want to be stealing too much of your medic's heals from the pocket and/or demoman. Scouts can use their speed to grab health packs in a way that the other classes cannot. If you have less than 110 health, then ideally you will go for a health pack in a SAFE POSITION so that you can get your health back up to 125 and by that time you will most definitely receive crit heals.
If you have less than 80 health, you should not be pushing forward but should be instead be in "panic mode", searching for a health pack (or the medic if you have crit heals).
Hopefully this clears up a lot of issues that you will run into when considering when is the best time to be getting a buff. Remember that buffing frequently is one of the most important skills an improving scout can learn as it will dramatically increase your performance (and reduce the amount of time you spend dead).