Oral = Spoken. So, you can only improve it by speaking as much as possible.
1. Speak to people near you who know English.
2. Find out language buddies on this website and add them to skype and actually try to have a conversation with them. Searching for people who are trying to learn Indonesian would be mutually beneficial.
3. Whenever possible, even when alone, try to say things you wanna say in everyday life in English. e.g. when you want a pen form someone, in your mind try asking it in English. This will help you think in English rather than translating it every time. This will make your English sound more natural and fluent.