This looks like a good start. There are several things you might want to do to make it even batter. First of all your rivers don't look too realistic. In the real world, rivers usually converge, not diverge. If they diverge they usually do that over short distances or over short periods of time. Reading
this thread might deepen your understanding of the river placement. The shape of your landmass doesn't look like something taken out of a garbage box, it seems quite nice to me, the coastline looks very natural and not simplistic. If you wish to try a different way of making landmasses you might want to try looking for example at
this tutorial by RobA (it's for GIMP, but could easily be translated into Photoshop),
this one by Schwarzkreuz, or
this one by OldGuy (there are many, many others of course, just search the forum^^). To make your map more alive and interesting I think changing the background would be a good idea. Take a look at
this thread where you can find wonderful textures by Coyotemax. I understand that you wish to achieve an antique look, the aged paper textures, that you will find there, will certainly help you with that. One last thing that strikes me as odd is the difference in the sizes of your trees. Making them a bit more uniform would look better in my opinion. To sum it up: I would suggest you take a look at the
tutorial section, you might find there a tutorial describing how to achieve a style you are after. Like for example
this one by Ascension for creating Antique-style maps in Photoshop. For Photoshop basics on the other hand, I find
these tutorials by jezelf priceless, there is a part in them on creating realistic coastlines too. Practicing your skills with the aid of tutorials is a nice way of learning new things and a good introduction into map making. You can later combine styles and make one of your own.
One last question: Are those white sections in the right hand corners parts of another landmass? If so, you might want to make them look more similar to your main one (but I suppose they are just not finished, right?^^).
Overall, a very nice map and a good use of brushes. I'm looking forward to how it develops.