Civilizations are a special type of SMP where players choose their own teams and lead them to victory. Each team had a unique advantage which the players can use to win the game and are a symbol of both tactical intellect, survival skills, fighting prowess, teamwork and deception.
Important skills to remember/master
PVP skill is incredibly important in PVP. Even if you have the best gear, a seasoned fighter can still overpower you even if they only have diamond equipment.
The second most important skill to learn is diplomacy. Diplomatic skills are essential in forging alliances with other people and make peace with enemies.
The third most important skill are survival skills. Survival skills not only involve foraging for food but also includes how to get the best gear as fast as possible, how to survive in the wild, etc. All of these skills are incredibly important to master. Thus it's more recommended if you sharpen these skills first before joining a Civilizations SMP.
Basic concepts and mechanics
Assuming you are now good at PVP, skilled at diplomacy and have good survival skills, we must learn the basic concepts of Civilizations.
Typically, Civilization SMP are divided into 3 or more teams, and the player can choose whatever their heart desires. In some competitions, the advantages lie on the team chosen, and the advantages/perks can either be resource advantage, terrain advantage or technological advantage while in other competitions, the advantages lie on which role the player chooses. The roles is dependent on the organizer of the competition so watch out and weigh the pros and cons of each advantage.
Another thing is how you will get stacked really fast. Depending on the civilization, there's no fixed way to get stacked, but one of the most reliable ways is through villager trading. However, some civilizations don't generate vanilla structures, only custom ones so look for other sources to stack up fast.
Another thing to know are who's gonna be your main enemies. In vanilla servers, opposing players are your main teams, but depending on the organizer, they can add NPCs that will ocassionally attack players. These hostile NPCs are usually deployed when the players' guard are low, providing them the oppurtunity to ambush unsuspecting players and kill them. At the end of the day though, opposing players are gonna be your worst enemy.
A thing you should look out for are the world events. Events typically include a famine or a disease, incursions from NPCs, revealing the coordinates for a structure that have good loot, leader election, where fighting between members are enabled, allowing for betrayals, exploration, building contests, etc.
Surviving in an actual competition
Assume you have joined the contest, what team are you gonna join? Determine which teams are available and make an in-depth analysis of each teams' strengths and weaknesses. For example, assuming the teams available are: Overworld, Nether and End, each team had its own advantages and weaknesses. The Overworld, has rich natural resources but are hidden in the depths and players had to mine for them which is potentially dangerous, the Nether had Bastions, thus gold and netherite, but the inhospitable environment can make it really hard for players to survive while the End, had the power of End cities and elytra, but the void and shulkers' levitation powers can make it a bit hard. Sure the End might be your best bet, as End cities contain the best loot in the game, but players join with literally no tools, so it's a bit risky. The Nether rivals the End with the Bastions, but the nether's hostile world is really challenging to conquer, so the best option here is the Overworld.
Assuming you've finally made it in, what are you gonna do now? First things, get wooden tools, make stone stools, and get iron armour and tools ASAP. Also aim for some diamonds and an enchanting table. Then get a full set of diamond armour ASAP. Not only it will make you more powerful and increase your chances of surviving, but also it can be used as a tool to recruit followers, as players typically ally those with powerful gear for protection and gear acquisition.
Look an eye for the world events. Set-up a basic food farm even if it's bread. Cows and pigs are a great foodsource and can help you survive in famines, unless you're underground