I need to find good locations to train because I want to do the main quest and the college of winterhold quests after I've unlocked the expert and master conjuration and destruction spells.

I play on Expert and want to switch to Master before I visit the greybeards and explore the Sarthal ruins.

So far all I've done is two side quests (promises to keep & golden claw), all civil war quests (twelve of them), the first four main quests, and the first college of winterhold quest. And I've done about a dozen bounty quests and only one miscellaneous objective: helping shadr in riften. I've killed about a dozen dragons too but I'm tired of waiting for them to appear.

Right now I'm level 17, Breton, and Conjuration/Destruction/Alteration are in the low 50s. Speech is in the low 40s and everything else is well below 30. And I've been playing for about 24 hours now.

Im not entirely sure what you mean by a place to train, this isn't like an mmo where there are levelled areas (though higher in the mountains you will find more scaled enemies). Theres ways to cast soul trap over and over again on a dead body to level conjuration (theres a youtube vid somewhere demonstrating it). You could possibly conjure something and then kill it with destruction if that is exploitable. Not sure theres too much fun it really.

I mean places with numerous enemies which respawn every few days or so.

Right now the only good place I've found is the Black Briar Lodge (promises to keep quest). The enemies there respawn but it takes about a week in game time which is really long. And their armor is very expensive so I can sell it off.

And I've noticed that the bounty quests are limited too. I can't get more than 4 or 5 from each hold and I'm slowly running out of holds...

Theres that glitch in the guy at the inn Riften that allows you to level speech quickly, is that the kind of thing you mean?

Respawns take longer in this game for that purpose....so you can't sit there and exploit it over and over again (though you can still do it even if it takes a week) for gold and skill ups.

Just play the game.

No, it seems to me he's talking about places where the enemies respawn, so he can clear the place again to build up skills.

Actually, they respawn in most forts and dungeons, but not all. Just check back at all the places you have cleared from time to time. Note that Bleak Falls Barrow respawns- have you checked that? Just the last boss doesn't. I don't know of any that respawn very quickly though. You just have to rotate through all the ones that do.

No I don't want to exploit the game by conjuring something and destroying it or using that guy in riften to increase speech because that is too tedious and boring.

I just want a list of places I can visit to kill enemies so my combat skills increase. Right now I just have the black briar lodge and waiting for dragons to appear... I might have to start killing guards but do guards respawn quickly??

Oh okay thanks I'll visit bleak falls again

Change holds, between all of them, you generally won't run out of bounty quests before they respawn. If you do... just explore. There are enough tombs\camps\dungeons\caves that there is no way you can clear out everything.

If you are looking to "grind" the skills, can cast soul trap over and over on a dead body for conjuration.

The other easy way to grind magic skills is to go to the Western Tower by Whiterun where you killed the first dragon.

There is a giant camp nearby. Aggro the giant, and lead him to the tower. He won't fit inside the door, so you are safe to sit and cast spells over and over.

It takes a bit, but if you advance the Dark Brotherhood Questline until you get Shadowmere, you can cast Flames/Frostbite/Sparks on him over and over to raise Destruction. I'm not sure about Conjuration/Soul Trap as I've never tried it. But I know that if you have patience you can boost both Destruction and Restoration with Shadowmere (just pummel him with Destruction magic, and then turn around and heal him with Healing Hands for Restoration).

enemies respawn in nearly all areas and even faster if the area does not have the cleared tag.

I just wish respawning didn't take so long but I just confirmed that bounty quests do become available in a hold after a little while so I'm happy.

You also have Helgen where you started the game. It respawns a handful of bandits.

Fast travelling also seems to give a 'here-I-am' effect on dragons. Very handy if you have some shouts waiting to be unlocked