I opened two screws (one on arm rest and another behind door latch) and one plastic hub below triangle.

I was wondering what else do I need to do to open Driverside front door panel of my 1999 Accord LX

 

From the point you're at right now:

Remove door handle and switch panel.

Pry off the triangle piece.

The rest of the door panel is held on by plastic clips. Start at the bottom and carefully pry the door panel off, working patiently. There's something like 6 plastic clips around the outside edges of the door panel, including the sides.

Then remove the door panel by lifting upwards.

 

Those little plastic clips that cover the screw behind the handle and in the door crevice (whatever it's called, right behind the window openers) are easy to break when trying to get to the screws.

If you do break one, just stop by the Honda dealer parts department the next time you are around there, it's only $0.75 or $1 for that plastic piece.

 

Yeah, I've broken 3 of them on my car...