Mining is a field with intense competition where some of them don't even pay electricity, with these conditions I would be surprised even to get even when investing in mining.
IMO the best way to invest on bitcoins is 1) to keep them and enjoy the enventual rise of price 2) to invest in some dicesites which have good ROI (but you're never truely same since they can close at anytime and you can also lose money in short term).
Can you suggest some trusted dice sites?
This website compares all dice sites (some of them have invest options and others don't). I would advise you two things.
1) Compare their activity, their wagered per day (very important) and the amount already invested (bigger invested amounts usually lead to less volatility but also usually have less return). With this data you can easily have an idea of how much you can win.
2) Ideally you should diversify between 2 or more sites. Some of these sites are online since a few years, but you still depend on their owner (If they wanted they could withdraw everything). Plus diversifying reduces the risk of a hard blow from a whale player.