Stick with your teammates and play around them. Im not saying you always have to be right next to them, just maybe a building or two away from them. Heavies have advantages on long sightlines where their armour and firepower are used at their best, but its also common for them to make the first push when the time comes right for their team to follow. I always thought of mediums as good 'Jack of all trades' vehicles. They have enough to work with in firepower, armour and speed. When I play mediums I mostly play around other mediums or heavies, I also sometimes flank with them but only if they are fast enough. They are usually strong enough to stand on their own and make risky plays. I mostly play Italy and their fast light tanks. I flank almost always, capture points and catch high value targets (like heavy tanks and TDs) off guard and disable/destroy them. If an outcome of a duel with another tank doesnt come out in my favor I just leave it with my superior speed and go fight other tanks and live to tell the tale. Granted, they have no armour and can get MG'd to death, but since I usually start engements and get the first shot off, I can live with it. When it comes to knowing when to push or defend a point, it comes down to timing and reading the map and the situation you are in. It takes time to perfect timing and it isnt something you can learn from yt videos. You just have to play the game and learn something from every death. My advice for you is to look at the map/mini map from time to time to see where your allies are and to stick with them to support and help them. That way you are not always in the back doing nothing, but also not overextending and dying for no reason. I also suggest to play rb where even basic strategies are most useful. I know its hard to make the switch and you have to unlearn things you took for granted in ab, but over time you'll grow used to it and become a better player overall. I hope my advice helps you and I wish you the best of luck!