You need a better understanding of the base game before you can think about the best macro decision. Also know that macro is about all the things that you should do in order to plan out for the long run. The final decision is always to destroy the enemy nexus, but how you get there is up to you. You need a strategy, and steps in those strategy.
Lets say you want to win by getting all the buffs and accumulating an overwhelming advantage. Most games are won because one team is just too strong and pretty much steamrolls the other team. So look at the objectives. Which objective is available? Dragon? up in 2 minutes. Baron? up in 1 minute. Okay, you have a decision to make, which do you go first? Here's a few things that can help you make those decisions;
wave management. Minions are easy to kill and they become easier and easier to kill as the game goes on. But stack a minion wave and that wave can take down turrets. So one thing to focus on, where are the minions? Are they top side? Great, a stacked minion wave top means that someone from the enemy team will have to go and clear the wave. If you go for dragon, its a 4v5 at best.
Enemy champions and key spells. Fighting a 4v5 is great, but wait the enemy has a shen. Shen can join a teamfight instantly. Maybe its best not to fight dragon afterall if its going to be a 5v5 when shen ults. Maybe it's not a shen, Maybe its a malphite. But malphite has TP, so he can still join the fight. Get a pink ward, clear the bushes, and start the objective so that if malphite tp's he has to tp to a weird location. If you don't feel confident, rush the enemy. Its currently a 5v4 in your favor if malphite is top, burn some summoner spells or key ultimates, then start dragon. Malphite can ult your team whenever he wants, but his ult is essentially wasted if there's no followup damage.
Enemy positions. You know that Malphite is top, but what about the enemy jungler? You see him botside, not good. Enemy jungler can attempt a smite steal, and has 50/50 chance of getting it. You're not comfortable with that statistic, so you set a trap. Go to enemy jungle, sweep a bush, and maybe you can catch someone. If no one is falling to your trap, be more proactive, force someone to show themselves by pushing another lane, maybe mid.
Items. one of the hardest things to judge is, will you win a teamfight with your team. Some champions have key item spikes, Lucian's first item is a huge spike for him. Same with Jhin. So if your ADC has more items than the enemy ADC, things are looking good. But wait, your tank doesn't have their mythic completed, maybe its not good. How about the enemy team? Is one enemy super fed? Maybe they all have their mythic items so that if you fight, you might lose due to item differences?
Warding. Where are your wards? Can you spot someone coming? Are there wards on possible flanking routes? Are enemies denying you vision?
Those are only a few things to keep in mind, but remember that macro is not decided on a single factor. Macro is culmination of EVERYTHING happening. Pro players will often plan multiple steps ahead. High elo players do this as well. In order to get a single objective, they will set up ward coverage for multiple minutes ahead of the objective even spawning. Some teams like to rush baron, so they will deny vision to the enemy top side jungle for like 5 minutes and keep the enemy guessing. Other teams will set up two pushing lanes and force dragon, which forces the enemy to either give up dragon or give up turrets. Some teams will start baron and send their midlane to push bot, which means the enemy team will either baron or an inhibitor turret.
Macro takes a lot of judgement, and is practically impossible to do well in soloq because everyone has different ideas on how to win. Maybe you think shoving lanes is the best way to put pressure on the enemy, but your teammate thinks sneaking objectives by setting ward coverage to catch enemies out of position is the best idea. So you two do different things and neither ends up working. Too many things happen, and what I listed are only a few factors.