Hum. Dyana.. which version of the 109 do you prefer to fly? The difference between the F4/G2 and the G10 is large enough that I fly them totally differently.
In the F4/G2, you are close to a turny plane. The F4 is actually a VERY good turner, and you can use that to your advantage (because most people will assume you are in a G10 and try to out turn you). The G2 doesn't turn quite as well, but it is much faster than the F4 is, so I think it makes up for it. The G10 doesn't turn well, in my opinion. You can use elevator trim to tighten up the turn some, but most planes will still outturn you.
If you are flying a G10, some good advice has already been given. Don't furball in it, that is a bad idea. If you are fighting a Zeke or Spit, use the vertical. Don't flat turn, you will not win. I wouldn't even recommend pulling a loop on the merge, because they can bring their nose around faster. Your best bet is either a slight climb as you extend away, to then make a gentle turn (2-3G) and come back at your leisure, or to make a climb straight up until you stall, then swing around and drop back on their tail. Which technique you use depends on how aggresive you are, and how much energy your opponent has.
Against an La7 in a G10- you are pretty much screwed ;-). IF you can manage to get the fight very low and slow you may have a chance. Against a Nik in a G10, the only move I have found that works fairly reliably is the rope a dope (climb straight up until you stall, then drop over on them). Most nikis will follow you up, and you will stall before they do, so you have to be very careful doing it. Best bet is to plan the climb so the Niki is about d700 away when you stall- he'll keep closing as you swing over, but he will be stalled by the time your nose swings around to point at him. Then you just have to be a good shot. This works on Spits to, and it is much easier.
Against the P51 in a G10- you really don't have much to worry about. Get the fight below 15k (I prefer below 10k). You can outturn a p51D and turn with a p51B. You can out accelerate both of them, although they are both faster on the deck. So your best bet is to plan the merge so you end up about d600 back, and just follow em as they try to get away. THey'll mess up eventually and you can close to within 250 or so to use your cannons.
Lastly- someone mentioned the LW cannons above. They are probably the hardest cannons in the world to hit with. The trajectory on them is absolutely horrible. My advice is the same as above- don't use them until you are within 300 yards, and don't go for the deflection shot. If you need to get someone to bleed off some speed so you can get within cannon range, use your MG's- you can hit with them out to 500 yards or so pretty reliably.
Hope this helps.
