Took a cursory look at your opening.
If you start out holding the 6 reds 3-points card, the first thing you need to think about is how to complete the hand as quickly as possible, which is usually done by either (1). Take 2 rubies and hold two more cards as soon as possible (and then buy the card with a gold gem), or (2). There is a level 1 red card on the board, buy it as soon as possible.
If you choose (1), then the next two cards you hold are better for buying other cards that need to be bought with red (since you already have red, you should use it to your advantage). In a game like yours, I would hold the 2-point white card (need 4 red, 2 black, and 1 green ).
If you choose (2), you should make sure that this level 1 red card doesn't go to your opponent, and you'll probably need to hold one more card in order to have enough (gold) gems to buy 6 reds 3-points. If I were you, I would probably also hold that 2-point white card.
If there is a red card of level 1 on the card market (and there are other high-value cards that need red), I would generally choose to prioritize (2).
You may watch your opponent in action. He holds a 5-Red, 2-points white card, and then a 6-3 points white card. This is a wise move because after he buys that white card, he can try to buy a 3-6 white card with the advantage of having one more white card.
In other words, you should try to buy as many valuable cards as you can (cards that can score more points with fewer gems) while using the bought-in cards to continue to increase your advantage.
Also, if you choose to hold lv2 or lv3 high-value cards (e.g. 5 stone 2 points, 6 stone 3 points, 7 stone 4 points) in your opening hand, you should try to buy them as soon as possible, especially the 7 stone 4 points from the lv3 hold, otherwise they'll be stuck in your gem position, unless you're simply trying to keep them out of your opponent's hands.
In addition, based on my experience, don't rush to hold these two level 2 cards of the same color (i.e. 5 stones 2-points and 6 stone 3-points) , because it is not easy to complete two cards quickly. In most cases, you can only complete one of them, unless your opponent is really weak and lets you take the green gems.
Lastly, watch the market every turn and try to maximize your advantage with the cards you have purchased. For example, in the opening round, there is a LV1 green card that was purchased for 4 stones, and then there are LV2 green cards on the market that are worth 5 stones 2-points, 6 stones 3-points, and also 7 stones 4-points LV3 green cards , all of which are high value cards. If I were you, I would choose to buy the LV 1 green and then try to buy these high value greens instead of the HOLD 6 stone 3 point black. This would also allow you to try and complete the Noble card. It's two birds with one stone.
