For double jumping to attack, you just need to learn to approach more carefully with lasers and SHFFLs. The reason that you start to double jump on the approach is because as people become more familiar with your Falco, they start learning how to handle your SHFFLs by hitting you out of the air, DD grabing, etc, and so by double jumping on the approach, you fake them out with the 1st jump and punish them with the double jump. This is the natural progression of someone learning to play advanced Falco vs. people just learning to play against said advanced falco, and it's a pretty common bad habbit. The trick is to know the spacing for when your SHFFLed nair or dair is safe as opposed to being punishable by the character that you're fighting against. Unfortunately, this is difficult to learn outside of experience, so the best advice I can give is to get your friends more involved or to get out to tournies to start learning what's safe and what'll get you killed.
The double jump's only true practicallity on the approach is when your opponent legitimately tries to go after your SHFFL approach and leaves you an opening to punish. This can only really be seen after you've double jumped (seeing your opponent whiff with an attack or a grab), so you need to have other options to fall back on after you've double jumped in case the opening is not there. On FD, there are no options, and if you double jump and the opponent doesn't screw up, you're in trouble. Your best bet is to DI away, waveland backwards, and hope that your oponent doesn't get to you first. On platform stages, it's much more practical, as you can set yourself up to waveland on a platform in case of a failed double jump approach.
I also failed to mention in my first post that you should start using edgehog -> bair on the edge gaurd. It's definately falco's most practical and safe edge gaurd and is particularly good vs. Fox. If you let go of the edge, double jump immediately, and then bair, you can regrab the edge, which is particulary good agaist Fox's who try to recover high. On a low recovery, droping from ledge to under the stage, then double jumping up to stage height with a bair out is the best option.
