For an intermediate investor, how would you recommend me to better my investment returns? What is an acceptable return % to you?

4-5% will be acceptable and realistic for the total portfolio.

40% or more per year how could that be realistic?

Increase your investment knowledge by reading as much as you can. An acceptable and reasonable returns would be somewhere between 5% to 8%. This return is also somewhat we can achieve when we invest in the STI ETF over a long time frame.

Cost is also a factor which will affect your over investment returns over the long term, go for good platforms allowing to the optimize your commission and fx fees. For me, a 6% - 8% return is relatively decent.

I would say 5-10% per annum is good to me.