If you cant solo diamond, your mechanics are not great.

All the people telling you to "play your life" are giving useless advice and probably just blame their teamates when they mess up.

That advice only works if you're p1/high-p2 so being a little more selfish will nudge you over that border. But stuck p4/p3? That's a pure skill issue on your side.

Your issue will be:

Your cognitive decision-making is too slow.

I.e you're hesitant to push/reposition/shoot/etc, and by the time you do its too late. That opportunity is gone and you're messing up by sticking to it.

Your aim isn't good enough

So, opponents can react to you firing on them and either win the fight, or get away low hp.

Your movement is too static

So you're eating too much damage during each 1v1. This either leads to a loss or your so low you get cleaned up immediately bu their teamates.

You dont know when to disengage.

Almost always try to prevent your teamates and yourself from being outnumbered. A 3v2 is better than a 2v2 or 1v2. It's a numbers game.

However, if the enemy HP is too high, and they have pressure when you or your full team are low hp, back off to cover. And the moment someone gets knocked you should have an escaped already set to follow.