Having a Home. Starting out in Hardcore is very similar to how you should act in Survival. Concentrate on being prepared for nightfall with a place to stay. Light level 7 and above stop monsters from spawning so keep areas lit up.
Gearing up. If your wanting to limit the amount of damage you will receive then Armor is the key. Move up as fast as you can from the Leather, Iron right through to Netherite Armor with enchantments.
Keeping your distance. Avoid close contact with your enemies by crafting a bow and attack from a far. Make sure this is not your only defence by having a backup sword and shield.
Dine like a King (or Queen). Players can die from starvation and forever become a ghost (Spectator). Not all food is treated equal so learn the differences. Build farms to produce all the essential building blocks for life (see what I did there!) Cows, Sheep, Carrots, Potatoes and others all make a balanced diet.
Mine for Rocks. Well not rocks, but Cobblestone. It has unique abilities to stop monsters by creating barriers or walls.
Don't go thirsty. Buckets of water are extremely useful for staying alive when you come across lava. Also good for creating barriers but useful to cool things down and soften landings by creating pools.
Like doing chemistry. Potions are essential for protection, healing and regenerating those precious hearts.
Have a plan B. Keep your options open by having more than one sword, armour and tools. But keep an eye on your inventory slots to allow gathering or your resources still needed.
Magic is real. Enchanting items increases their usability and often your life. There are plenty of defensive, offensive and utility enchantments to make use of.
Run away. This may sound simple but staying away from trouble can often be your best strategy. Be prepared by taking your time to upgrade, protect, repair and if needed fight another day.