I try to make at least a few remarks about each type of endgame. Of course you can (and people have) written volumes of books on the endgame. This is a quick and dirty overview with just what came to mind.
Pawn endgames:
Require concrete calculation. Check king activity before trading into it. Protected passer > outside passer. Protected passer can also compensate for lesser king position. Opposition is only useful to breakthrough to a rank/file.
Knight endgames:
Few general principals. Botvinnik "Knight endgames are pawn endgames" meaning concrete calculation, outside passers are strong (knights are slow) and they're unforgiving of mistakes. Only pattern I can think of is knight fork deflection and fork defense.
Deflection:
Fork defense thing
Knight vs rook:
Some fortresses exist. Strong side makes use of zugzwang. If pawnless then it's a draw except for some positions where weak side is trapped in a corner or along the edge.
Bishop endgames:
Same color bishops:
Keep pawns of same color as bishop (just like mid game). Can put on same color if squeezing opponent to death though.
Opposite color:
Can put bishops on same color for possible fortress (pawns can't be attacked by enemy bishop). Otherwise absolute passive defense is dangerous as always.
Bishop vs Rook:
Some fortresses exist, but not if your pawns are on the same color as the bishop. Strong side wins with use of zugzwang. If pawnless then weak side king can head towards corner opposite color of bishop.
Minor piece endgames:
1 extra pawn usually not enough to win.
Knight vs bishop:
Bishop likes pawns on both sides. Bishop likes pawns off its color (as always) Knight likes pawns on one side. Knight likes to force enemy pawns on same color as bishop. Some knight fortresses involve a blockade on squares that are the opposite color of the enemy bishop.
Rook:
1 pawn only:
Knight and rook pawns can draw easily with passive defense. King and rook on backrank with King on queening square.
Other pawns need 3rd rank defense or other assorted defenses (e.g. rook behind, rook in front). To win need philidor, short side/long side stuff, etc.
If king is cut off by 2 files it's usually a win (not for knight and rook pawns though).
Bishop + Rook pawn vs no pawns is a draw but difficult.
Two rook pawns vs no pawns can be a draw but can be difficult.
Connected rook+knight pawn with king cut off can win but some theoretical positions are very difficult.
There's a horde of other technical positions.
General remarks:
Rook > King > pawns. i.e. can always consider sacing pawns for rook position. Improve rook before king. e.g. you'd rather your king blockade than rook.
3 vs 4 on one wing is draw but difficult.
4 vs 5 on one side is a win but difficult.
3 vs 4 with one outside passer is a draw or win and very theoretical and difficult. Useful to blockade passer with rook as soon as possible.
Queen:
If just 1 pawn:
Center pawns win unless enemy king in front.
Flank pawns can be drawn with perpetual even if defensive king is not in front. Defensive king runs to opposite corner to reduce queen trade forks.
Multiple pawns:
General order of importance goes king safety (perpetual checks on exposed king is the great equalizer), queen activity, and passed. pawns. e.g. passed pawn with active queen will win unless perpetual available.
Queen vs rook:
Pawnless is a win, but can be very difficult.
with 1 pawn there is a well known fortress. You must have either a knight pawn or a pawn on the 7th rank. The only exception is a rook pawn must be on the 6th. However even the breakable fortress is difficult to break, and I think most sub masters (and maybe most masters too) just assume it's a draw regardless of pawn placement).
As the title suggests, I'm looking for general guidelines about endgames. Some simple examples of what I have in mind are that rooks belong behind passed pawns, that a rook can't stop connected passed pawns on the sixth rank, and that opposite colored bishops are drawish. I'm hoping for some other guidelines in situations that don't have a theoretical solution, like a queen and knight vs. queen and bishop with a few pawns for both sides.