It's really something that you just get to know with time. After reading so many hundred katakana words, you begin to see the patterns, but here are some rules that generally apply:
R's before consonants generally don't get pronounced, but instead just lengthen the previous vowel (e.g., archive -> アーカイブ)
V's at the end of words tend to turn into B's, while they sometimes stay as V's (ウ's with dakuten) when at the start.
Words ending in D or T tend to gain an extra O because in the T/D "row" of kana the ト is considered to be a closer approximation of the English ending consonant than the ツ
Although I wouldn't recommend using this as a guide, check out Psy's posts in this topic:
http://www.japanesepod101.com/forum/vie ... php?t=2438
The other posters don't quite use Katakana as the Japanese do, but Psy's is spot on, and I'd recommend reading his post for an idea, as well as just maybe reading more with a lot of Katakana words (I know that technology articles tend to be Katakana saturated)!