Making a model in PhotoScan works like a reverse panoramic. Instead of taking photos from a point, you are taking them of a point. Since everything that follows is based on these photos, this step is absolutely critical. If you do not get this right, you are setting yourself up for a giant headache and/or a second photo session.
Similar to a program that stitches pictures together for a panoramic image, PhotoScan needs at least a 30% overlap between your pictures to make sure it can figure out their orientation. When photographing an object like a headstone I like to do one ring at a high angle, one at the middle and one at ground level pointing up. Also, do a series of shots linking the high angle to the low. This will help to ensure PhotoScan can connect each pass together.
A high quality camera, and the skill to go with it, will allow for higher quality models and final textures. However, you can get some excellent models from point-and-shoot cameras (like in the above image) or even phones! Which you will use depends on what is available, the conditions, and the purpose of the model.
If your camera allows it, I recommend taking photos in the RAW format as this is uncompressed and lossless (otherwise JPEG works). PhotoScan cannot use RAW images directly, so you will then need to convert them to TIFF files before you can import them. I use Camera RAW for this, though I am sure there are other programs you can use.
PhotoScan does not deal well with sharp changes in lighting or white surfaces that are too bright. You will save yourself some frustration by making sure your lighting is as even and flat as possible. This means that photographer lights will help indoors. If modeling outdoors, take your photos around sunrise/sunset, with cloud cover, or using tents or tarps.
Having your photos in sharp focus is critical to a successful model. Any picture where your subject is blurry should be deleted as it will only cause problems. A monopod or tripod will help you avoid this issue to begin with, especially when photographing small objects up close.
Depth of Field
This refers to how far your focus goes beyond the focal point. I will let you look up further discussion about this, but essentially, if your depth of field is too narrow only part of your subject will be in focus, if it is too broad then the background will also be in focus. Neither of these will necessarily kill a model (unless working with a fixed camera position), but they will at least result in unaligned photos, or lots of extra points from the background.
This will depend on the size of your subject and the level of detail you are going for. More photos will allow for more detail to a point, though there are diminishing returns. I typically shoot for around 70-80 as a standard, though I have made some good models with as few as 40 pictures.
The key is to make sure each photo has the needed minimum 30% overlap with the previous one. You will learn how many you need with some experience. Do remember though, 1,000 photos will not do you any good if your pictures are bad.