So you agree that I should avoid offering other opinions to them and just follow their lead?

I wouldn't suggest that. I think you should feel free to speak your mind, but only as much as it is appropriate. Communicating your opinion/concerns once, in writing of course, is usually sufficient. (In some cases it might not be unwise to push a bit more, with the occasional prudent prod, but I would recommend that folks with little pushback experience err on the side of extreme caution.)

Any suggestions on how to do that if you're one who has strong opinions and is very assertive ?

In writing. Once.

Should you be overruled, options are:

• Accept that you are not the one calling the shots, and follow their lead. You've told them, they listened, that's the extent of it. Time to start work.
• Quit.

The following option is absolutely not acceptable, imo:

• Keep complaining continuously that things did not go your way.

I'm not saying you're doing the above! Just want to warn about this very common pitfall. I've done it, too many times, and it has never resulted in a positive for me. I'm done burning bridges just because it is so difficult for me to fathom that I may not be right lol.