Performance
Separate graphics from connection
If the world stutters but blocks and chat update normally, the problem is usually local rendering. If movement rubber-bands while the frame rate stays smooth, the connection or the server is the likely cause.
Test one change at a time
Lower render distance first, then turn off fancy graphics, then cap the frame rate. Note the result after each change so you know which one actually helped instead of stacking every optimization guide at once.
When the server is busy
Lag can come from your connection, your computer, or a busy server. Check the Discord for announcements before changing your setup. A restart of Minecraft is often enough to clear a temporary stall.
Need the address immediately? Open the server IP reference. For menus and setup, follow how to join Unstable SMP.