Learn how to make coordinated turns, keep your eye on the ball and don't let the rate of climb indicator drop into the negative when doing flat turns. Besides not having a wingman, that is one of the most common mistakes I see people make in a turn fight. Giving up their alt and widening their turning circle because they're actually in a shallow spiral dive. I guess because they're thinking if they go faster they'll turn tighter.
It's a little more complicated than that as it's totally dependent on your starting airspeed and Corner velocity. Corner gives you your best possible turn rate and smallest turn radius so that's what you're aiming for. If you're significantly above your corner velocity you will improve your turn rate by a nose-high turn (nose above the horizon) to allow you to decelerate to Corner at the same time you're trading your speed for a bit of altitude. Once you near Corner then overbank slightly to bring your nose down just a bit below the horizon and trade some altitude to sustain your turn rate at Corner plus, since there's a vertical component to your turn, you can reduce your turn radius even more than a flat turn at Corner. This is known as a "wing over." If your starting speed is below Corner then make the entire turn slightly nose-low (nose below the horizon) to trade a bit of altitude to sustain what turn rate you have and gain a bit of speed to come closer to Corner. How much "nose-high" or "nose-low" you go depends on how far away from Corner you are (and it takes a bit of experimentation and practice in your chosen ride.) If your Corner is 225mph and you're going 400 then bring your nose well above the horizon, even to the point of doing an oblique pitchback. If your starting speed is 200 then use only a slightly nose-low turn (5 to 10 degrees). The slower you are the more nose-low you need to turn (a slice). If your speed is significantly below Corner, say you're climbing out at 150 when you get attacked, your best option is probably closer to a split S. As in the nose high turns, you have a vertical component to nose-low turns but it works against you. A nose-low turn at corner will still give you your best turn rate but your radius will begin to increase as you're working against G so, generally speaking, you need to be judicious in nose-low turns to prevent your radius from getting out of hand. You can control for this just like the nose-high turns by starting very nose-low and then rolling to bring your nose up a bit once you reach corner changing your turn into more of a low yo-yo.
In summary, use nose-high and nose-low turns (and combinations of them) to maintain your speed as close to corner as you can be.
