I hated Higher French, but then, I had a teacher who was pretty rubbish. Lovely woman, but rubbish teacher. And also, my class was really big for a Higher French class, so yeah... Plus I didn't really enjoy Standard Grade French, so maybe taking it at Higher was a bad idea for me :P
The NABs are fairly easy. The Reading ones are so simple, you just need a good dictionary. And you need to memorise a pre-written essay for the Writing NAB, but you can have a sheet with 40 words from your essay in front of you, to help you. Listening's a wee bit difficult, though my French teacher advised you to write notes during it on what the people are saying, and answer the questions during the two minutes at the end of the excerpt. And as far as I can remember, there isn't a Speaking NAB.
It's important you make sure you have all your essays you've written over the year thoroughly memorised, as any of the topics in them could come up in the exam.
The Speaking part of the exam is 25% of your final mark, though I don't know what the others are.
And we didn't get a folio of work, like in Standard Grade.
I'd recommend buying the Leckie Higher French course notes book, though your school library might have it. It's really good, and it has lots of phrases and stuff for each topic, and little exercises throughout to help you memorise stuff. And it also has a Directed Writing section and a section on preparing for the final exam. There's also a book with tonnes of Directed Writing exercises and useful phrases to use in them, but I can't remember the name of it.