Right before bringing asparagus to the oven, spray cooking oil on the tops of asparagus. Moving the oven rack closer to the top of the oven will also make asparagus crisper, but you would want to check on it to avoid burning the asparagus. Another option is to broil it for 1-2 minutes at the end. Again, you want to make sure you don't burn the asparagus if you do this.