TALK TO THE GEOTECH! provide them with the project information you know (or think you might know). i've had so many instances where critical information was not revealed until the exploration was almost complete. knowing estimated loads, finish grades, settlement tolerances, oddball things (isolated heavily loaded areas, settlement critical "things", etc), etc. if you happen to have a particular area of interest or you think the plans may change (building location moving, final grades changing, etc), then mention that to the geotech. otherwise, let the geotech locate the borings and depths. keep the communication channels open (going both directions) to help the project progress efficiently and effectively. and as far as choosing a geotech, get one you or someone else knows and trusts. they might cost a little more than the cheapo geotech but it's more often well worth it. the cheapo might be able to give you an exploration for a thousand bucks less but then they throw in recommendations that add many many times that to the overall project cost...or they completely miss something because the workscope was so "slim" and the project ends up spending more money than originally anticipated. go with a reputable geotech firm.
if you happen to have MSE walls at the site, the wall designer (since they are designing geotechnical structures) should direct that portion of the work (boring locations, drilling depths, test frequency, general evaluation of settlement and internal/global stability, etc). in my opinion, the drilling, testing, evaluation of the mse walls and their construction should be included in the wall designers package so that the owner doesn't get contractually stuck with the wall designer's liability. as a geotech myself, i'm not going to take their liability (and i don't think it's professionally appropriate for them to dump the liability on the owner)...before i take their liability, i'd just design the darn thing myself and get paid for it if i'm going to be responsible for the thing.