Strong flame: A tall, full flame is a positive sign, expressing the vitality of the magic working in your favor.
Weak Flame: Your work may lack passion, or else forces such as luck or an adversary may be opposing you. If the flame remains weak for the full duration of the spell it may indicate that the condition you wish to achieve will come to pass only with much effort on your part.
Erratic Flame: When a flame repeatedly alternates between burning tall and low it may indicate conflict. Perhaps you are actually uncertain that the target of your spell is what is best, or else another person may be working against your will.
Active Flame: A flame will jump or flicker when seeking your attention. The difference between an active and erratic flame is that the former is strong. Meditate on your intentions, and address any spirits you have asked to aid your spell to see if they are speaking to you.
Dead Flame: Magic is not working for you. The forces at variance to your will may be stronger than the energy released from your spell. Evaluate your goal, and perhaps try a different approach or spell.
Sparking flame: This may be another way for the spirits to get your attention, or the spark may represent barriers that are being blown up by your magic. Typically a positive sign.