The cornerstone of good singing is correct breathing. It should be very low and relaxed. Stand up straight and relaxed with your ribcage slightly elevated. Place your hands firmly at your sides at the bottom of your ribcage. Your thumbs should reach around toward the back of your ribcage while your fingers should wrap around to the front. Take a deep breath. With normal and athletic breathing, often your ribcage expands. The goal here is the opposite: Keep the ribcage as silent as possible and expand the muscles around the midsection. When you do it correctly, your hands will push out, and it will feel as if the air is filling up that low space like a balloon or innertube that wraps around your waist. Now hold this "outward" position of your midsection as you exhale and gently tighten your lowest abdominal muscles inward. Eventually, your midsection must collapse, but hold it as long as you can. This "inflated" or "held" feeling is the position to sing in, and is commonly referred to as support.
When it comes to the actual singing, it is not difficult if you have the breathing down. Simply envision the tone coming from the middle of your head and let it "speak" very naturally as you sing. Don't add extra weight or color, let it be very free and easy. Control the tone with your support and breath. Gospel and spiritual songs often involve more chest voice than other styles. Once you get good at "speaking" the tone and supporting it with breath, you can add more chest voice by intensifying the breath support and singing louder in your speaking range.
Gospel and spiritual songs are sung in a freer, more rhythmic manner than most other musical styles. When singing them, feel free to take liberties with the tempo, rhythm and melody to suit your interpretation of the song. Don't take too many liberties--listen to famous singers perform these songs to get ideas about the correct style and boundaries. If you read music, get sheet music of the songs you want to sing and learn the exact melodies and rhythms before you change them.
Most importantly, you must feel the song. This musical style is very emotional, whether happy, sad or somewhere in between. When you sing, give each word or phrase must have meaning and the overall "theme" of the song must be felt at all times. You must connect with the emotion in the song to be successful at performing it. This will also give you more satisfaction while you sing it. Any liberty you take with the melody or additional runs or flourishes must also be inspired by the emotion you feel. Read the lyrics and research the history behind the song to give you more personal inspiration.