I bought Av Xpress about 2 months ago and im finding it really hard to remember any of the keyboard shortcuts! Its really slowing down  my editing speed and it looks a bit unprofessional wen i take ages to either click through the process or when i mess up the keyboard shortcuts. Does anyone know any tips or tricks on how to remember the shortcuts easier/quicker?

Here are the keyboard shortcuts for Media Composer. With very few exceptions, your shortcuts should be pretty much the same.

You could invest in a color-coded Keyboard also. 

But, I'm a firm believer that repetition is the best memory device.  So, just use the shortcuts and use them often. 

As a lazy hunt and peck typist moving constantly between Avid and Protools I use colour coded keyboards. 

For my mapped F keys I have made up (in Illustrator) narrow keyboard sized printouts on thin card descriptors for my F keys and another of my shift F keys.  I trim these to fit on the keyboard above and below the F keys. These are easily moveable when I switch between Avids.

Yes, either a color coded keyboard (preferred) or adhesive key cap labels will be a huge help committing those to memory.

Hey so i had a similar problem around 6 months ago and my lecturer at uni linked me to a company that sells sticker sets and silicone covers that go on your keyboard. They have all the shortcuts for avid printed on the keys so u dont need to remember anything! It has sped up my editing time 10 fold and now when im working for clients i can breeze through the shortcuts with out any pauses
you should definitely try it out

www.editorskeys.com

But apparently only for Mac keyboards, none for PC?

I would remap the keyboard to the way you like to work. Set it up in a way that makes sense to you and then it will work the way you expect it to without having to get your head around someone else's idea of a good keyboard layout. 

This may not help you too much in the short term, but I found a good way to remember the shortcuts is to repeat the letter of the key in your head every time you press it.  It's a habit I got into in my early days working with Avid.  I set up my keyboard the way I liked it, then every time I would execute a command sequence on the keyboard I would think to myself what the letters were instead of the command.  I came to think of my extend edit button as P for "pull", my overwrite button as B for "build", my match frame button as N for "Natch Frame" (my M key was taken already! ), and so on. 

While I had keycaps on my keyboard originally, I soon got to the point now where I no longer need or care about having a color coded keyboard, since all of the commands are letters in my head.  The extra benefit is that I can rapidly string these commands into sequences without having to think about it.  For example, to extend the head or tail of a clip I park the playhead where I want it and type GIP or GOP.  To trim, I do the same thing and type TIX or TOX.  It almost becomes more like typing than pushing individual buttons.  By thinking this way my speed has dramatically improved.

yale:

repeat the letter of the key in your head every time you press it.

That's great advice and I suppose I sort of have done the same thing although not quite deliberately.  For example, I have F8 as my Subclip, but SHIFT+F8 is Match Frame, mostly because I think the icons looked similar enough to me.

But some others I have are

• F5 for Filler (using the "F" sound for association)
  
• SHIFT+F5 for Add Filler to Start
  
• F6 for Audio Mix(er)
  
• P is for Locator (because I call it a "peanut")
  
• ? = Find Bin.  
  

there are probably more, but I can't think of them right now.