You could try "你最近還好嗎？" or perhaps "你最近怎麽樣？".

In fact, 'ni hao' is already casual enough, because it only contains two words. Still, 'ni hao a' is a little more casual than 'ni ao'. If you really need a casual way to say 'ni hao', actually you can just say 'hello, hi' in English. It feels very casual to our Chinese people.

when you meet the person for the first time.you should say "ni hao" .however, if the greeting between friends, you can say "fan4 chi1 guo4 le ma1 ?"(it means do you have the meals?but please notice, it doesn't mean that you invite him/her to have meals togher.)

well....lxstudy's answer is "xiang feng dian dou xiao,wo shou wen ge hao,xiao rong gua mei shao" THT's answer is"ni zui jin hai hao ma？“and "ni zui jin zen me yang?" if the friends haven't seen each other for long..we'll say.."zui jin guo de zen me yang?最近过得怎么样？”

相逢点头笑, 握手问个好,笑容挂眉梢