I just started playing Rocket League again over the last month after stopping around the end of Season 3. After doing some training and practice matches, I calibrated at Gold 2 and have quickly worked my way up to Platinum in comp standard. I'm hoping to get to Platinum 3.

On a side note, I didn't even realise there was a solo standard. I would've played that otherwise as I'm always solo.

My two tips would be:

Train and Practice

I've got 137 hours on Steam but only ~17 hours worth of match time. I spend a lot of time doing training packs and freeplay exercises. I structure my training a lot like the stuff in this video. At a minimum, being able to 80% the default all-star goalkeeper training is a must (GK skills are most important imo). If you can keep your goal clear and hit basic aerials, you should be able to get to gold.

I do 30-60 minutes training/practice daily. I am a massive fan of Poquito's custom training packs.

Play Defensively

Unless it's an open goal or easy shot, the half way line should be your boundary. Cross it with caution, and try and get back to your half ASAP. Most players in the lower ranks chase the ball and don't do rotations. Playing a 'sweeper keeper' type role minimises counter-attack potential and allows you to hit the ball back into the opponent's half if your teammates' attack breaks down. Always stick to this role. The exception is if you happen to have a teammate who is getting back too.

It's all well and good being able to shine with a good team around you, but it's not often a bunch of randoms create a great team with perfect synergy. Play the less glamorous role, foundational role and wait for the opponent to make a mistake. Because they will. And most randoms can score the easy shots. You'll know when you're getting good at this role because lots of easy follow-up shots and set-ups will start opening up to you. Especially in Silver where entire teams are out of position after one attempt on goal.