Hi TS, if let's say you are a beginner and you like to chant
mantras, try to choose those that are short and easy to commit to
memory and hence easy to attain concentration on. But of course, if
you still think Shurangama
Sutra is the right one for you,
then by all means do your best to recite it
wholeheartedly.
Other than that, I think it's best not to neglect reading more
books that give you a general but clear introduction about Buddhism
and Buddhist practices. Attend more talks for beginner buddhists if
you can.
Buddhism is something that one needs to understand and practice
at the same time. It's like a chicken and egg thing; without
understanding, your practice becomes mere routine and you will find
yourself wanting to give up at some point in time. Without
practice, you can't understand the concepts further with your mind
and heart. So Buddhism requires both understanding and practice at
the same time.
All the best for your cultivation. :)