In fiction writing, it's generally considered good practice to dispense with dialogue tags completely when it is clear who is speaking. However, in cases where you do need to use them, try, wherever possible, to stick to a plain verb, rather than adding an adverb. Here are a couple of examples:
1) He said softly
This would be better rendered as 'He murmured' or 'He whispered'.
2) He walked quickly
Here you could go for He dashed, He hurried, He hastened, He strode etc.
See how the single verbs pack more punch and add some flavour to the narration? The choice of verb is important. Think of the different sense of the scene you get by choosing 'he dashed' over 'he strode'. The first has a feeling of urgency; the second imbues him with purpose.