Its different every time, and you know youre entering trouble when you get that "you shouldn't be doing this..." sort of feeling! Thats a bit abstract, but if you don't feel confident, don't attempt it. Short lines are reasonably straight forward provided you prepared well, your DA, Max VNE and wind considerations and HOGE limitations.
Long lines are completely different as the reason you have one on, is for obstacle clearance. Because you are on your own, you have to pay a lot of attention to obstacle clearance. You are most always on the limits of power, but smooth cyclic control is the key, unless you really look, you don't move the cyclic much, its just pressure control. Large cyclic movements can make the load move a large distance, and in a tight area thats the last thing you need. Precision lift is even different again, those pilots do it for thousands of hours and Im not that experienced in commercial precision lift, just drill rigs and pipes etc..
If you get a chance, contact Helog, or Rotex in Switzerland, they do that stuff like we have breakfast. The first thing I would do is get the sling endoresment with a school that specialises in that, or your check pilot. Helicopters are extremely quick to do the opposite to what you want, as you know, and in sling loading, its even faster, and as roundwego says, can be high risk to you and those on the ground. Planning is very important.
Have a good chat with an instructor and grab some slings, chains and shackles and go and practice looping some simple objects on the ground,also practice guessing the weights of objects, for instance, a ride on mower, a portable generator, or five railway sleepers tied together, you get my drift, its a very satisfying thing to do when you do it well. Out in the boondocks, when youre on your own it helps, youll be amazed how good you get at guessing weights, then checking them on the load indicator. Good luck