Both goals should be realistic and preferably based on historic values. Use Adspert’s hints to pick plausible values, and drive the performance of both goals towards your end goal in steps.

Do no change either of the goals too often. Much like working with only one goal, the algorithm needs time to adjust to its new reality, and that doesn’t change by adding on a 2nd goal. If anything, it’s even more important to change the goals only when truly needed and in small increments (see previous point).

Try to combine volume (Cost/Day) and performance goals (Cost/Conv, ACoS, ROAS) whenever possible. To offer an example - if you choose a Cost/Day main goal and an ACoS second goal (or vice versa), then Adspert will attempt to reach the ACoS goal, but at the same time spend at most the amount provided in the Cost/Day goal. Once the Cost/Day goal is met, the algorithm will maintain it, meaning the ACoS goal would not be met exactly, but pushed as close to the goal as possible.

Don’t worry about which goal is Main and which 2nd.