The municipality of Oberschleißheim is located in the north of Munich and can be reached via the motorways A 92 (exit "Oberschleißheim") and A 99 (exit "Neuherberg") and also via the roads B 13 and B 471.
In front of the New Palace there are about 120 free parking spaces for cars. Coaches may also be parked here.
How to get there by public transport
Take the train to Munich central station, then the suburban railway number 1 (direction "Freising / Flughafen") to "Oberschleißheim". From there it's about 15 minutes walk to the Schleißheim palaces; you can also take bus number 292 (only on workdays) to "Mittenheimer Straße" or "Schloss Lustheim".
You can watch my 3 min 15 sec Video Munchen-Oberschleissheim-Munchen by car out of my Youtube channel or here on VT.
It is very easy to get to Oberschleißheim with public transport.
The line S1 of the excellent suburban train network (S-Bahn) of München, direction Freising, takes you from the München Hauptbahnhof (Central Station) to Oberschleißheim. There are trains every 20 minutes.
When you arrive in Oberschleißheim, you have to walk for around 15 minutes to reach the area of the castles. I did it under the sun at more than 30 °C! It is easy to find the way, since it is often marked.
Oberschleissheim is accessible by the S-bahn from Munich. Take the S1 line from downtown Munich to the "Oberschleissheim" station.