I have 12 months' worth of salary in savings. Now, should I invest everything after expenses or continue saving a portion of my monthly salary and invest the remaining amount?

There are a couple of options you can do.

1. Put 6 months of your salary in a high interest yet liquid saving account such as singlife, gigantiq, singtel dash and invest the rest including the 70% of your salary moving forward.

2. Same earlier steps as above but invest 40-50% of your salary and keep the rest in cash savings in also a high interest liquid savings account to start preparing for your warchest, which will come in handy when the market is down and you want to inject more funds to take advantage of the situation to average down your buy in price.

With a savings account it can be difficult to beat the inflation rate.

surely you should first read a lot on investing, which then really is a good option when you can 'park' your funds untouched in a brokerage account for at least 15-20 years. This, because stock market investing was possibly the best performing asset allocation over these long time intervals historically.

here is a beautiful primer for novices:

https://sias.org.sg/wp-content/uploads/pdf/SIAS...

and here I have written up, what not to do with your money:

https://seedly.sg/questions/what-is-your-genera...

If you really want to invest into stocks,

possibly the lowest risk and best diversification mode is via an

MSCI World ETF

or

MSCI ACWI ETF

have mentioned advantageous example ETFs in the link.

GOOD LUCK with investing, and always be careful with recommendations your bank or insurance advisors give you, conflicts of interest are inherent in finance industry.