As Michau said, it depends on your use case. User6726 and Michau have provided a good overview of scholarly/lossless transcription systems. But since you mention specifically transcribing for English, there's another option.
If your goal is to have the word pronounced (something vaguely like) properly by English-speakers, or to use a name in an English work, then using common letters might be more important than being able to reconstruct the original Arabic from your transcription.
In this case, you could use a lossy transcription, merging similar letters together and using familiar English digraphs.
For example, both د and ض are very close to English "d", and it takes significant practice for English-speakers even to tell them apart. So for an English-speaking audience it can be easier just to write them both as "d" rather than introducing and explaining "ḍ".
If you want to go this route, I'd suggest:
- ع → [nothing]. /ʕ/ is unlike anything in English, and using a half-ring or "3" will just confuse most native English speakers.
- غ → "gh". This is fairly standard for the /ɣ/ sound, and as a bonus, the digraph is completely unambiguous in Arabic!
- ر → "r". Nice and simple.
- ك → "k". Same sound as in English.
- ق → "q". Unless it's before a "u", it should be clear that this is the "foreign sound sort of like a k" one, as in "Iraq".
- ء → [apostrophe]. Glottal stops are better known than /ʕ/, and the apostrophe is common when transcribing them in dialects (as well as in Hawai'ian and other languages).