This is pretty good for a first attempt, although I have a few suggestions for how you can improve it.
Forests: the forests would look better (in my opinion) if you
--include tree trunks where the rivers cut through them
--include scattered trees around the forest rims, getting scarcer and more dispersed the further from the forest edge: most forests don't simply stop, they gradually peter out (unless farming is included)
--perhaps you could include pockets of forest growing in the mountain valleys (which matches how actual forests grow)
--another thing to consider is making the forests less dark. I don't know the best way to do that, but either reducing the opacity of the forests, or using a lighter green, might work.
--perhaps you should add shadows to the mountains. If using Photoshop, I would add shadows by getting a brush with low opacity and low hardness, and simply painting over the shadowed parts of the mountain ranges (on a new layer, ideally). You can then play around with the opacity of the layer, and set it to Multiply (or experiment with other blend styles) to give it the right look. Adding shadows will make the mountains seem more 3-dimensional. You can also use shadows to emphasise some valleys over others (by making the deeper valleys darker or bigger)
--reduce the opacity of the ridge lines and (if it isn't too much work) perhaps make them straighter. I always recommend using GoogleEarth to research things when mapmaking. Check out the Alps, or Himalayas, to get a sense of how mountains look from above.
--there's a bit of a problem with the western mountain range where it splits into three branches. The middle branch looks (if you don't mind me saying so) plain wrong. I'd remove it altogether, if it was mine, and keep the other two.
--you could try to make all the mountains look more rugged. The best way to do that (again, in my opinion) is to redo the valleys as I suggested above (i.e. make them straighter), but make the central ridge of the ranges curve around a lot more. This website has some diagrams that might help to show what I mean (especially under "Drawing Realistic Mountains").
--I also think you should add hills to the landscape. This might, in fact, be the most important suggestion, because as it is now, it looks kinda flat (literally) apart from the mountains. Hills will make the mountains blend into the landscape more realistically, help to define the courses of rivers and locations of lakes, and can also be useful later for placing towns/cities and roads.
Rivers: all new maps on this website tend to get carefully scrutinised by the River Police, but as far as I can tell, your rivers check out. The lakes do look a little odd, but adding hills, as I suggested, may resolve that issue a bit. Other suggestions
--the delta looks peculiar. I don't know how to describe it, so instead I'll just direct you to GoogleEarth again. The Nile is the classic river delta to check out.
--you could work on the shape of the rivers a little bit. Rivers are often described as having a life cycle. When they first appear in mountain valleys, where the channels are narrow and steep, they run straight (youth); by the time they reach the sea, they have eroded wide valleys, and so they meander very widely (old age). It is a useful model to remember, and is shown in this diagram.
I think that's probably enough from me for now. I hope you find those suggestions helpful rather than unnecessarily critical.
It's also good to see another Aussie joining the site, too.