I almost always use soft solder (stay brite #8). (And I deal with systems with 1000's of refrigerant.) As everyone said here, heat evenly and let the heat draw the solder in. A bubbly solder is usually too much heat. For the small sizes you're praticing on, you do not need a flame thrower. Learn to use a smaller 'soft' flame and 'play' with the heat. Do not linger the flame on a particular area for long.