Emma, I take my own pictures for my listings...I will tell you three things...
1) Get a Sigma 10-20mm lens (on your D300 this will be 15-30mm)...does not matter for the f-stop most of the time I shoot at f5 to f7....
2) Use a hotshoe flash with a bouncer on it..Gary-Fong or a Soften defuser...I use the generic ebay one's for $6.00...
Ebay listing....
3) This is the most important thing...most people show-case the furniture not the room...the furniture shows depth, placement, and size...but try to get more in each shot...so that you get the feel for the room...
These shots were taken with Sony a900 and Sigma 17-35mm the a900 is a FF camera so there is no multiplier...shot at 17mm with a slight crop....
OK now the photography stuff...don't be afraid of moving peoples furniture around...to make the room look better....also take lots of shots...you can always discard the bad ones...If they insist on you taking shots the way they have it...take one there way and one your way...they usually shut-up...don't mean to be rude...but it's your time not there's....and lastly...make sure you know what your particular MLS requires for the picture size/dimensions and most importantly amount of pictures...mine in Houston HAR only let you post 16 photos.....
Personally...I try to tell a story front-entry-dinning/living-kitchen-breakfast-family /great room-backyard-master-master bath-then anything left over I post the other bedrooms...don't be afraid to show multiple angles of the shot...give a better idea of the room...or yard space...
If you have any other questions...post here or PM me....it might take me a little bit to get back to you...but I will...
Good Luck...