It's as simple as this: When they come up in a random draw or when you put them down intentionally, just consider them as generic spread positions, such as:
- The blue Influence cards signify a general influence on the situation...not a pro or a con or an underlying influence...just something that's an influence
- The orange Character cards signify an unidentified or unknown person, or they're describing someone you may or may not know, depending on the context they land in
- The green Topic cards can be used as a wildcard topic (something the cards want to talk about), whether they show up in the beginning of the spread or in the middle
- The purple Timing cards can be used to determine a length of time. So say you get the four of pentacles, maybe the timing is four days, four weeks or four months...whatever your process is.
- The red Outcome cards could signify a generic outcome (even though we have a labeled card for that) or it could be an interim outcome
Of course, you can make them anything you want. What I wrote above were just examples. Whatever you decide is cool, whether you're consistent with it or not.
A different thought I had was that when they come up in a spread you draw at random, they could like parentheses in the middle of reading, giving you a reason to stop and talk about such-and-such a person and how they relate to the reading (or such-and-such influence or timing or topic or outcome). So they might be used more like a sub-discussion in a reading. Or when they come up, you can put them to the side and use them in the same way when the main reading is over.
Another thought I had is that they might signal a place in a reading where, once you've read the card prior to it, that you could, based on what was revealed, then ask a clarifier question to give more information in regards to time, topic, whatever. When laying out your spread, you can wait to pull a tarot card for that position until you know the intent of the meaning you want it to convey.
Holmes also suggested that when you draw a blank card, you can draw another spread card to place on top of it to read as a compound position. So, for example, you draw the blank character card. So draw another spread card to place on top. Like What to Avoid. Now that position becomes about a person you might want to avoid in regard to the reading. Holmes says that whenever they do that, they somehow manage to choose a card of the same color to place on top. So a What to Avoid Influence card on top of a blank Influence card. So you can decide that if that happens, it just makes the reading of the card in that position extra important, like "whatever you do or learn from this reading, be sure to remember to avoid X, Y or Z".
Or you can just attach whatever meaning or intent occurs to you in the moment. With all the yap in the cartomancy world about the right way of doing things and the wrong way of doing things, I hereby proclaim that there is no wrong way to use your Deck of 1000 Spreads. Even if you choose to use them as kindling for your fireplace. So if anyone ever tells you you're not doing it right, send them to me. I get final say in the matter. :D