Roleplay means to play a role. Inexperienced players are going to have trouble playing the role of their character. Many become disgruntled with character development and prefer to play dungeons and dragons as a hack and slash game.
Encouraging character development
Allow the players time to get the game mechanics down. Once they can spin that d20 on the edge of their character sheet you can look at building the character.
Darvil the Sword: Fighter (level 3); neutral; 10hp; St(14), In(13), Wi(9), De(18), Co(3), Ch(16); Equipment: Sword(1d8), leather armour, boots, belt, pouch. Description: Sickly, Darvil coughs up blood after one turn of physical activity and requires three turns to recover. He chews chillies he keeps in his belt pouch and undertakes breathing exercises to recover after he coughs up blood.
Some time around third level ask the players to come up with a phrase that their character uses regularly and the circumstances under which it is used.
Personality: Darvil tries to speak on most things of concern to him and thinks the more input the better. He will say the words: "Damn it..." when he needs to cough up blood.If the player remembers to use the character's 'phrase' add a few experience Points to the character in reward. Don't give it away. The player needs to say it to get the experience.
Low charisma characters are less likely to input, while high charisma characters will speak more. So penalise a high charisma pc for not producing character input equal to the charisma bonus penalise low charisma PCs for oversharing their life story. Darvil's player needs to provide input at least twice to avoid an exp penalty and saying 'damn it' twice won't cut it.
With Darvil coughing up blood with every profanity, and offering to let the kobolds live if they cough up their gold more to avoid exertion than out of any sense of kindness we have a character that is more than a sword.