Short version: you find words you recognize, and that will give you the key to any unfound letters in the word, which should make some other words possible to identify - repeat until you can read it entirely.
The hard part is identifying words at the beginning, when you don't have any letters filled in yet. For that, the most common tricks are to look for 'a', 'and', and 'the'. Any one-letter word is going to be 'a' or 'I', and any three-letter word that occurs frequently is probably 'and' or 'the'. That can help you get your first couple of letters. Double letters and other patterns can make other clues, as can apostrophes.
An example:
Maybe roleplaying games are more your speed? Then you're in luck! You can come play in the demo of the Sentinels of the Multiverse RPG a few times through the convention. More information coming on this in the next few days.
I noticed the 'a' after 'RPG', which gave me:
a__ a a a__ ____ ____ _____? ____ _' __ ____! ___ a ____ _a __ ___ ____ __ ___ _________ __ ___ __________ ___ a ___ _____ _______ ___ __________. ____ _a ______ __ ____ __ ___ ____ ___ a.
After that, I guessed that 'erg' which repeated several times translated to 'the'. This gave me:
a__e e__a a_e a_e ___e ____ ee? The ___'_e __ ____! ___ a __e a __ the e __ the e_t__e __ the __t__e__e ___ a e t__e th____h the _e_t. ___e _at ______ __ th __ the e_t e a.
Notice the 'The_' which I bolded. That is most likely 'They' or 'Then'. I guessed it was 'then' (actually, the possiblity that it could be 'they' didn't occur to me until just now), and that gave me 'n's:
_a__e __e__a__n a_e a_e ___e ____ _ee? Then ___'_e _n ____! ___ _an ___e a n the e __ the ent_ne __ the __t__e__e ___ a e t__e th____h the __n_ent__n. ___e _n____at__n __n n th n the ne_t e a.
The 'ent_ne_' that I bolded began with a capital letter. I managed to guess that it was 'Sentinels'. That gave me 's', 'i', and 'l':
_a__e __le_la_in_ _a_es a_e ___e ____ s_ee_? Then ___'_e in l___! ___ _an ___e _la_ in the _e__ __ the Sentinels __ the __lti_e_se ___ a _e_ ti_es th____h the __n_enti_n. ___e in____ati_n ___in_ _n this in the ne_t _e_ _a_s.
You get one guess what "Sentinels __ the __lti_e_se" is. That gave me o, f, m, u, v, and r. After that, there're many words that are easy to pick out, and you can fill in letters at your leisure.