when i started playing i just had 12 in each army and used the 3 lines sistem let them deplet their javelins throw them into the fray once they get tired or very tired pull them back behinde the 3rd line and move in the 2nd one

also works wonders in defense and their vast amount of javelins does make a serious dent on enemies with bellow average armour (3 lines add in peltastai or archers beteween the lines to increase the shock value ) imagine as you advance against them the amounts of javelins rainning down on you increasing most troops will be near breaking point at that stage so if you use it near a patch of trees imagine being surrounded by peltastai placing themselfs behinde you and hitting you on the back (the patch of trees ofc serves for cover to let the enemies go by without noticing your peltastai)