hard 改为harder
整句的翻译：我要更加努力来提高我的英语会话能力.
still可以用来修饰比较级,相当于even,可译为“更”、“还要”、“甚”.
例句：
(1) We must study still harder.我们必须更加努力地学习.
(2) It was cold yesterday,but today it is still colder.昨天天气很冷,可今天却更冷.
(3) Her sister is still taller.她妹妹个子还要高.
(4) They came still earlier.他们来得更早.