Good news and bad news about this one:
The good news is you do NOT have to do every song in the game on expert. This lets you bypass some of the bastard songs, like Raining Blood. You only have to do the last song.
The bad news, of course, is that the final song is none other than the infamous Through the Fire and Flames. You have to beat this on expert bass, guitar, drums, and vocals.
From easiest to hardest (in my opinion) are the instruments and tips:
As nickb2819 said, if you can't do this song on bass, just throw in the towel now. If you can't do it, you won't be able to do it on guitar, therefore just go home now.
Dragonforce isn't about powerful vocals, there about badass guitar solos. Therefore, there isn't much singing in the song, and you can likely mumble your way through it, humming the pitch. I'm a ridiculously bad singer, but I beat this on my first try.
If you could do this in Guitar Hero 3, you'll have NO trouble here. The intro and outro are all tap notes this time, making them a hell of a lot easier. For the intro, just have a rubber band holding down the green button and then tap the rest of the pattern. Beyond that, it's not so bad. Remember to go into practice mode if there's a part that's kicking you in the junk. But beyond the intro, it's pretty straightforward.
The HARDEST: Drums.
This song is, to be brief, an endurance on expert drums. No matter what you do, you'll need a hell of a lot of stamina to get through this one. Most of the song is the same pattern (Y+pedal, R+Y, etc...) with a lot of rolls, and the occasional constant bass kick (picture a lite Expert +). If you can't do expert drums, quit now.
But, if you have the stamina, I found a trick to this: overhitting the notes doesn't hurt your Rock Meter as much as missing does. If you have two bass pedals, you're perfect. Just keep going boom-boom-boom on the pedals, at a steady rhythm during the main parts. At the same time, consistently hit BOTH the yellow and red pads. This is VERY tiring, but it's great if you're like me and simply cannot get the fast pattern down.
Dont be afraid to pause too. I'm sure I came close to collapsing from exhaustion doing this, and my method is extremely tiring. However, it works.
If you are using the rock band or guitar hero drum sticks, throw that crap away and get some real sticks. For doing rolls, I found those are as useful as dog turds. Real sticks are heavier, and as a result, your rolls are more fluid AND you don't have to apply as much force to the pads while drumming, therefore reducing the amount of energy you use.
In closing, bass and vocals (and guitar to a degree) are fairly easy, but may require practice. Expert drums seems to be the one every stuggles with, and unless you are a professional drummer, you WILL get tired. My method WONT get you a good score, but it'll keep the rock meter in the green the whole song.
Good luck, you'll need it.