Hi Bob,
I'm in no way a native speaker, but here are a couple of tips that I worked out myself:
Vowels are often added in writing to modify the consonant - that is, you see them but you don't say them. Think of the "s" sounds in "Suí sios". If a consonant its in the middle of a word, it is sandwiched by either by two slender vowels (i, e) or two broad vowels (a, o , u).
The other confusing thing is adding the "h" (it used to be a dot!). This always changes the pronunciation, but we can still recognise the original word in writing.
Also, you'll see that "buffer consonants" are added for euphony. Compare "sráid" to "An tSráid Mór". Again, the spelling reminds us of the original word (much like the "odd" spellings in English) but the pronunciation changes. Your tip here is the "N" sound.
Hope that helps!