Before you order at an Indian restaurant you’re not familiar with, you need to get an accurate read on spice and heat. No one wants flavorless fare, but one person’s medium-spicy is another’s incendiary — and vice versa. While servers can make recommendations, first-hand experience is how most patrons come to know a chef’s set-point for spiciness. At Punjabi Tadka, the second northern Indian restaurant in Arlington Center, many of the dishes are good, even if not full of the spicy heat we crave.