Твóрог or творóг?
How do I know which pronunciation is right without looking it up in the dictionary?
Russian language exhibits paradigmatic accentuation: there is a number of accent paradigms, or models, which are defined by some aspects of the word origin, and are closely linked to the word formation paradigms.
These paradigms are described in Zaliznyak's works, most notably in От праславянской акцентуации к русской. It's about 400 pages of dense text.
Most basically, there are three accentual paradigms in Russian: baritonized (accent always on root), oxytonized (accent never on root), and mobile (accent anywhere). I could expand these further but would end up pasting the whole work.
Concerning творо́г / тво́рог: there is a tendency in modern Russian to move the accent towards the beginning in mobile words.
For some words it has long since been a norm: во́здух, же́мчуг (the old accent is preserved only in the idiom благорастворение возду́хов)
For some words it's not a norm yet but few people are aware of correct pronunciacion: дабы́, апостро́ф (almost everybody reads да́бы and апо́строф).
For some words it's not a norm but more and more people are using до́говор, зво́нит, вклю́чит instead of correct forms: догово́р, звони́т, включи́т.
Words like тво́рог / творо́г, и́наче / ина́че, о́бух / обу́х are in the middle of this process, and for them both forms are considered correct.
There are some rules and some "less strict" rules, where you have exceptions and they represent a tendency, rather than a rule. So we have patterns, but they have exceptions, of course.
In any case there aren't hard rules so that "you're always sure". You'll slowly come to know what's the right stress after you start acquiring some Russian vocabulary but this will come from experience rather than learning rules... But I'll try to give you some advice:
ё: when you see this in a Russian word, the stress is always on it:
ребёнок, её, актёр, Фёдор, ...
For this rule, you can be sure this is 99% true, the only exceptions are borrowed or compound words where it could change.
-ий/-ый: These endings are almost never stressed (unlike -ой in большой for example):
великий, сердитый, ...
-ческий: Usually the stress doesn't fall on this "part", but on the syllable before it (again, there are exceptions).
социалистический, мелодический, ...
First person singular, not in the first conjugation, such as Читать, but in the other conjugation, it tends to be on the last syllable:
- смотреть - смотрю
- звонить - звоню
- хотеть - хочу
- любить - люблю
- читать - читаю
- делать - делаю
- спрашивать - спрашиваю
- and so on...
-ие and -ия: Words ending like this, generally have the stress not on this syllable but on the previous one:
упражнение, приглашение, образование, ...
Some exceptions could be:
требование -> требовать
разглядывание -> разглядывать
Words which end in -ия:
-ство / -ость: These endings are not usually stressed:
чувство, гражданство, яркость, ...
There are always exceptions in this case, too.
In case of творог, both pronunciations are common and standard (i.e. correct). In the general case though, I am afraid you will have to look up in a dictionary; there are no rules. In many languages the stress is bound to a certain syllable (e.g. in Slovak it's always the first syllable, in French and Armenian always the last). In Russian, the stress can fall on any syllable.
first: крас- ненький, second: кра -сав- чик, third: красо -та, fourth: искусство -вед
One could make up certain rules, or patterns, regarding a very small set of words, mostly borrowed, but I don't know if it would be of any use. For example, words ending in -ция are usually stressed on the preceding syllable:
му -та- ция, ассоци -а- ция, про -дук- ция, ин -фек- ция
As an example of another rule one could say that words ending in -логия, -графия, -метрия are stressed on -лог-, -граф-, and -мет-, respectively.
The problem of stress is further complicated by the fact that different grammatical forms of the same word may have different stress.
Я хо -жу. Ты хо- дишь.
ед.ч. во -да; мн.ч. во- ды
The stress is considered one of the most difficult aspects of Russian. When learning a new word, it's best to memorize its pronunciation along with the pronunciation of its different grammatical forms. It's a lot, I know, but then no one said Russian was easy :)
As far as I know there are no general rules. In the case of
творог, I think the stress varies by region. In Ukraine I have quite often heard it with the stress on the first syllable.