The anacrusis attack does not present great problems when the note or the chord that comes before the beat is of the same length as one of the notes that follow. But when the note in front of the first beat is not as long as a one beat we might have difficulty in giving the attack.
Often an inexperienced conductor gives a very sharp stroke to indicate he beginning of the performance. This is not the right way: first of all we add a beat which is not included in the music, and also we might create a typical misunderstanding between the conductor and the orchestra: the one waiting for the other.
The conductor, gives a first stroke and waits for a reaction from the orchestra, meanwhile the orchestra is disorientated because it is waiting for the second stroke which indicates the exact timing.
The result is that the orchestra starts playing in an indecisive manner and with a complete lack of precision.
The best way is the following: give a very simple beat attack but make a visible preparatory gesture