One of the challenges of real estate photography is to prepare photos for upload to the local MLS in such a way that the uploaded photos look their best. A related consideration is that you'll want the photos to also look great on your client's broker site as well.
One of the evils you'll have to live with is that every MLS is going to run your photos through an automatic "photo mangler" to make sure the photo specifications are whatever the MLS geeks feel is right. MLSs are different so I can't tell you for sure what your MLS is going to do to your photos. If you are in the greater Seattle area (NWMLS ) you can upload any JPG up to 3 MB. Then, regardless of what the pixel width is the photo is it is reduced to 400 pixels wide (aspect ratio left alone) and then severely re-compressed (JPG compression). I recommend you take the time to research how your local MLS processes uploaded photos so you understand exactly what you are up against.
What can you do to make your photos will look their best? Here are some suggestions:
Even when you follow these steps the fact that the MLS systems are going through another JPG compression after you upload is going to make the photos look worse.
I highly recommend that you make a habit of looking at your photos on broker sites and the MLS if you can get access so you are aware of what the final photos look like. In the end, one of the biggest arguments for providing a tour/slide show with every shoot is to be able to present your photos better than the MLS and broker sites do.