Should I tell players what they do wrong?

I don't either. But I was meaning a mature summary of key points in a game rather than put downs or boasts or insults. I take it from your articulation that you have no faith whatsoever in any player's ability to give constructive criticism/help.

I have no problem accepting this when I lose otb. It seems that correspondence chess is different, which is curious to me when someone could have put weeks or months ionto a game.

correspondence chess has many resources available during play...otb does not...so players can find their own insights into a game if they so wish...dont need a 'know-it-all' comments...unless asked for

One has to be real careful or he or she can hurt or offend an opponent by giving un-asked for comments or advice.  I made that error with an opponent I had gotten to know a little and liked and enjoyed playing.  He's been polite and responds to questions or comments I make, but there's a coolness that has been present ever since I made what I thought would be a disguised comment to help.  Bothers me to have done that and I apologized to him and will never do something like that again.  It makes sense that if a player wants help or advice, he or she will ask for it.

I can't speak for everyone but, personally, I would welcome this type of interaction, rather than be insulted by it.

If a stronger player wants to give some suggestions or ideas after the game, I will take them with a smile on my face. I wish more players would offer their experience or knowledge in this way.

linuxblue,

some people appreciate it. however, some don't give a crap about their mistakes they just look for weaker opponents who fall into their favorite traps so giving advice to such players is pointless

I have had some post - game analysis here with correspondence players. That is also a nice OTB tradition in some parts.

I sometimes ask for analyisis when I am losing or offering to post the opponent my analysis when I have won. If everybody is friendly then this is not a problem. If people chose to act in a negative way, they are just missing out on opportunities to learn or to pass on knowledge.

Caps lock ? Um. Should I give advice about not doing that ?

I am certainly not a chess coach. There are people on this site who are better at chess coaching than I could ever be such as Valeri Lilov.

I think that there is a distinction between rather perfunctory feedback and help over a continual timespan which would be coaching.

Generally I would be all open for advice if I got outplayed by my opponent in a seemingly equal position. What did he see that I missed? However, at present I am mostly in the bad-blunder stage, so from these I can usually feel the effect immediately on the board, hahaa!

I like how they great ones do it after their matches (say at the recent Candidates). In the subsequent Q and A session, they talk openly about what went on. Also, in the livestream of the present FIDE GP in Zug Switzerland, one could see Radjabov and Leko sit for several minutes at the board post-game, chatting friendly over a hard-fought draw. It looked very natural and relaxed. This is how it should be, in my opinion, independently of whether one won or lost. For me it would be normal to have a post-game chat. Of course it depends on the other person as well, if he is inclined for it.

Tell ur opponent the mistakes he made only if he asks for it.

If I were there, I would surely ask my mistakes and discuss abt the game.

Always give advice, but add "I think" to make it look more friendly. Example:
I think you could have made a stronger move then Nf5, there's too many weaknesses and now the knight is far off.
I, and any reasonable person, should not take offense but learn instead.  
Especially give advice in correspondence since that is more serious than a random blitz game. 

Nah don't be a dick mate.

of course, all advice comes AFTER the game. You could just send a friendly message whether the opponent is interested in post mortem discussion.