Dynamics and articulation are really important – they help establish the character of your melody. The example below gives a sense of the level of detail you need to include. Students tend not to put in enough of the two and three notes slurs that give Classical melodies their characteristic shaping. The boxed text tells you how to input the various dynamics and articulations in Sibelius.
Lots more on instrumental techniques on the Texture and Sonorities page (e.g. pizzicato, sul pont. etc.).