Making your own blast crater is a nice project to get away from painting the minute details on your Blood Angels. Get yourself some paper clay that will dry itself and you are pretty much ready to go.
Open up your pack of paper clay and get shaping. Design how you want your crater or anything and let it dry. This may take a day or two or three depending on humidity.
The next step can by done in a myriad of ways but I prefer to just mix your main paint color for your crater (I used red brown here) with white glue and small gravel pieces with a sprinkling of sand too. This is "textured paint" for our purposes here.