Welcome aboard! ta0's right...
Concentrate first on getting your top's center of mass (CM) exactly at the "contact" (support patch). If not too much wobble, the "pointer" (end of stem opposite contact) will then be happy to follow "guides" of many different shapes -- not just spirals.
Now have several working LEGO versions of this spintoy with a number of different guides, but it took a lot of guess-and-check to get there, and it may be the same for you. If I had to do it again... (Search this forum or Wikipedia for unfamiliar terms.)
Step 1. Pick a design with at least 3-fold rotational symmetry and make the built top as rigid as you can. In Tim's example, the 3 evenly spaced hanging balls reduce the top's overall rotational symmetry from infinite (circular or axisymmetric) to 3-fold. This design's plenty rigid -- partly due to the chosen material, and partly due to the bell's double curvature. However, suspect that it could also work in wood or stiff plastic.
Step 2. Bring the built top into good static balance by adding mass to its "light side" or shaving mass from its "heavy side". (Many practical discussions on this forum.) Physically, this brings the CM to the symmetry axis. Balance each structural level separately, as in Tim's top, and you'll likely have enough dynamic balance to avoid most wobble.
Step 3. Shift CM along symmetry axis to coincide with contact by adding, subtracting, or shifting mass without breaking your dynamic balance. With Tim's design, you might just slide the bell along the stem before fastening it down.
Test CM height by observing what happens after a smooth release...
1. No consistent horizontal drift in pointer direction => CM at contact. This absence of precession is the goal for your finished top.
2. Precession in same direction as spin => CM above contact.
2. Precession in opposite direction as spin => CM below contact.
Precession direction and absence of precession are easy to observe and very sensitive to small CM-contact offsets.
One last point: Guide following (mainly a matter of rolling with or without slip) will suffer if there's too much hopping due to wobble.