The phrase “first of” doesn't have a specific, standard synonym. However, if we break it down and consider “first” and “of” separately, we can analyze some possible equivalents.
“First” can be replaced by words like “initial”, “foremost”, “primary”. For example, “the initial step” instead of “the first step”; “the foremost consideration” instead of “the first consideration”; “the primary goal” instead of “the first goal”.
“As for” or “regarding” could sometimes be used instead of “of” in certain contexts. For example, “First of all” could be rephrased as “Initial considerations. Regarding this matter...” or “Foremost, as for this issue...”.
In conclusion, while there isn't a direct synonym for “first of”, by analyzing the individual words and considering alternative expressions, we can find ways to convey similar meanings in different ways depending on the context.