(I think/I really think) you need to/must/should ...
How about ...?
It is usually a good idea to ...
My suggestion/advice is (to) ...
Why don't you ...?
You could (try) ...
You probably/definitely/really should ...
Have you tried ...?
I (would) (strongly) suggest/advise that ...
If I was/were you, I'd ...
In my experience, ... works really well.
It's generally best/a good idea to...
One idea is to ...
One thing you could/should/have to do is ...
The best/most important thing (to do) is to ...
.. is worth a try.
A (self-help) book I read recommends ...
A piece of advice from ... that I'd like to pass on is to ...
A wise man once said ...
As the proverb says, ...
I can't recommend ... strongly enough.
You should ..., no doubt about it.
It might be an old wives' tale, but ...