Four or five, tied well, beat a dozen you cannot remember on the bank. Wet the knot. Seat it. Trim the tag.
Eyed hook or swivel
Grinner / uni
Thread the line through the eye, form a loop alongside the standing line, wrap five or six turns through that loop, wet, seat against the eye, trim. The knot you will use most.
Hooks with no eye
Spade-end whip
Lay a loop along the shank, whip six to eight turns towards the spade, pass the tag through the loop, pull the standing line so the loop buries, trim. If it slips, you whipped the wrong way.
Changing a hooklength
Loop to loop
A small figure-of-eight or overhand loop in the hooklength, a loop in the mainline, one through the other so they seat like two chain links. Faster than retieing every time the maggot crowd bites you off.
Hair-rigged wafers, corn, boilies
Knotless knot
Hair the length of the bait plus a bit, stop on, bait on, whip five to eight turns up the shank, tag through the eye away from the point. A hair so long the bait waves is as wrong as one so short the bait sits on the gape.
Slider floats
Stop-knot
A few turns of a short piece of line or powergum around the mainline, tightened so it grips but can be moved with fingernails. Rubber stops are kinder if you have them.
beginner
Essential knots
The grinner (uni) covers eyed hooks and swivels. A spade-end whip covers hooks with no eye. Loop-to-loop lets you change a hooklength without retieing the world. The knotless knot hairs a wafer or boilie.
Wet nylon before you pull. Seat against the eye. A long tag is safer than a tag that slips. If a knot looks ugly, cut it off. The full set with uses is on the Knots page.