For informal speech you might want to use "ajmo", e.g. "ajmo na ples", let's go dancing. For comparison, "ajmo" is like "ikuzo" while "hoćemo li" is like "ikimasen ka?".

It's the same. Hoćemo "form" is used more often in my opinion. Be careful with hoćemo. It literally means to want. It would be more grammatically correct if you would say : Hoćemo li pjevati pjesmu?- Shall we sing a song. Hoćemo pjevati pjesmu. We want to sing a song. In everyday speech we often omit that li, if the meaning is understood. For ex.: Hoćemo ići na kavu u tri. It is actually a statement but with proper intonation it can be a question:). You could also say: Hoćemo li zapjevati pjesmu? Shall we sing a song ?-it's not used often. :)