Hi!
First of all, when you gen a world, you get that phase where it is finished and not saved yet, right? You can move around the cursor on the map. Use that!
I always check whether I got the civs I want BEFORE accepting a genned world. To do so, I move over the map until I find an Elven Forest Retreat, a Goblin Dark Tower, a Dwarven settlement, and a Human settlement (note that dwarves and humans may conquer and use forest retreats and dark towers). Note that the map icon does not tell you who lives there, but if you place the cursor on top of a settlement, at the top of the screen, you will get the general information, including the race actually dominating the place.
While not that helpful, there is also the thing that when you embark, your home civ's settlements will be marked in blue on the world map (the right map). So, if your civ is extinct, there will be no blue settlement markers on that map.
In order to support dwarves, you need large mountain chains as that is where dwarves like to settle. Also keep in mind that they need neutral mountains, so good and evil zones are dangerous. Also note that the default settings for caves (not the cavern layer!) are a bit on the numerous side, increasing the odds of racial extinction, so you may want to decrease that number as well.
Deathworks