2 stoke tips

250 or 125

Well... hmmmm... If the revs fall, kick the shifter down. When you run out of power from over-revving, kick the shifter up. If your revs are low and you think you can get them up again quickly, then clutch it a little bit. But if you don't think clutching is gonna do it, kick the shifter down. You have to know your bike as to how the clutch feels, when you don't have enough gas, when you are over-revving, how fast it can rev up, what gear you should probably enter this corner and what gear you're gonna exit in (and yeah, you might be shifting mid-corner) and when you're gonna shift and then downshift for the next corner.

I "got" the clutch once I started treating corners like a start... I do my braking, move from standing to sitting, and then power into (as much as I can) and out of the corner, feathering the clutch as needed to keep the revs up, just like I'd do on the start.

You can away with less clutching and shifting on a 250, but on a 125, you're gonna be shifting pretty much constantly and keeping a finger on the clutch almost constantly, too. See my signature.... I can't even ride a 250F because my instincts are screaming "shift!!! clutch!!! shift!!! clutch!!!" I ride 450F's and think "why do I even have more than 3rd gear?"

I suppose it just takes a TON of practice. I've been doing this for 45 years or so and I'm _still_ working at it. Work at it every time I go riding, every corner, every straight away. I PRACTICE at it, too, which is a lot different from riding.

There's a reason why 2S's are a little more challenging!!!!

If the motor is not reved up do something different

Try to find a flat area to ride. Work on understanding when the power comes on in the revs & how wide the powerband is on the engine when shifting through the gears. Once you understand where the power is work on shifting through the gears while clutching in the meat of the power. That should keep your momentum going. Try to stay off the rev limiter at first till your ready to open her up. It will take some patience & practice.
Once you get comfortable with using the clutch & going through the gears hit up a safe track to practice the technique on a more challenging terrain with small jumps, ruts, corners etc..
Stay safe..