I humbly offer a few of my personal 'tips' for reading, not just with the Marseille, but any deck that doesn't have pre-conceived meanings illustrated on the pip cards.
TIP #1 - Define 'reading'
What are you doing when you read? Is it a Jungian 'free-association' method? Are you attempting to predict the future? What is it EXACTLY that you are trying to do here? Know and commit to whatever it is. Define it for yourself, and be able to explain it to your 'victims'. If the querent is wanting to know which horse to bet on, and you can only give advice about why he has a need to gamble, you need another querent, and he needs another reader. Always let your querent know what sort of 'reading' they'll be getting, and don't be afraid to decline a querent if his inquiry doesn't mesh with your 'style'.
TIP #2 - Be a Sponge
What ever your approach to the cards, research.. research.. research.. You do not need another novelty deck. You need more books. If you want to use the cards for divination, research it. How does divination work? What are the common threads in Astrology, Palmistry, Geomancy? When you find an interesting idea, hunt down its 'root'. "Ah, SIX is symbolic of harmony." Now go find out where this idea came from, and when you know, ask yourself if you find this reason valid or not! Don't take Levi's, Crowley's or Camoin's word for anything. Check it out yourself!! If you're taking a Jungist approach to reading, GO READ SOME JUNG! If you are one of these 'hyper-spiritual' beings, and have a direct line to the divine - aka "I read intuitively!" and think research is unnecessary, you stand corrected! You need to research the phenomenon of intuition! How does it work? How can you hone it?
TIP #3 - Imitate, Assimilate, Innovate
Once you have the appropriate 'knowledge bank' initiate a little I.A.I.! Don't fall into the trap of thinking of innovation in the modernist/socialists' misinterpretation - as a destructive process. Cherish and use the tradition. Build on our ancestral knowledge base!
TIP #4 - Qualify
Qualify and rigorously test your methods. Keep what works, and discard what doesn't. I use the Tarot mainly as a predictive divination tool, and have little or no interest in 'consoling people, or telling them how to solve their problems. I attempt only to give objective predictions, so I can only speak of qualifying methods to that particular end. An easy method of qualifying predictive divination methods is to do a daily reading on the following day's weather. Keep doing this until you can correctly predict the next days weather for one month straight. I would consider this a bare minimum of qualifying before attempting to do predictive divination for anyone other than your cat!