The first thing to remember is that ablative absolutes are used instead of a subordinate clause, and so usually have a temporal, concessive or causal meaning, which is why they are often found at the start of a sentence. You have to, therefore, identify which the sense of the ablative absolute is; if it's temporal, [e.g. literally 'with the sun having risen'] you should reflect that in the English, using words like 'when' and 'after' and then translating it as if it were a simple temporal clause. If it's causal [e.g. literally 'with all hope of victory having been given up, (they surrendered)'] then words like 'since', 'as', 'because',' given that', etc. work well. For the concessive sense [e.g. literally 'with their city walls surrounded, (they kept on fighting)'] words like 'although', 'despite', in spite of', etc. can be used.

Literal translations of the Latin do work and will get the marks but almost always seem clunky and uncomfortable in English and don't show fluency or true understanding, which really is the aim of translations.