Hi Antony. and welcome!
First, Tamiya Desert Yellow is a bit dark for an Abrams in desert camo. the colour is much more washed out, tending to hints of grey.This model:
is, I think, fairly close to the real thing. Don't ask ab0ut the penguin. It's a long story...
There's no single way of achieving this finish, but this method is fairly widely used. It assumes you're using an airbrush, and that you can use it to apply paint fairly precisely.
First, look at photographs of the subject of your model, and decide what sort of colour you want it to end up as.
Start by priming your model in medium grey, medium brown, or black.
When this has dried ovenight, spray the model in a darker version of the base shade. You'll probably need three light coats to get a good coverage, and spraying the model panel by panel is a good idea, so that, towards the edge of each panel, the primer shows through. That's why many modellers use dark primer coats. In your case, Tamiya Dark Yellow works well as a darker version of the base colour.
Then take your base colour and spray that, keeping just away from the edges of each panel. The idea is to make each panel look slightly lighter towards the centre than it does towards the edge.
Repeat this with a lighter version of the base colour, again, concnetrating in the centres and away from the edges. Next, take a yet paler version of the base colour (maybe the previous colour, with about 30% pale grey or buff (Tamiya Deck Tan works well for this) amd gently spray a thin coat from above, trying to reproduce areas which have been bleached or lightened by the sun. Notice that, with all these last four stages, and assuming you're using acrylics, you only need to leave a few minutes between coats. I often do them all at one sitting. However, you need to leave the model at least overnight before the next stages
At this stage, decals, and washes/ filters often applied. We'll pass over this stage for now, except to seay that the effect is often to make the finish darker.
Therefore, you now apply a very light, thin, overspray of the lighter version of the base colour. Apply these coats from a distance, and check your work after each stage. the idea is to stop just before you think you've made it too light.
As an example, conider this AFV Club Sd.Kfz.II, which is supposed to be in overall Dark Yellow. the actual colour is nowhere near as dark as the Tamiya version.
You can see darker colours in the shaded areas, ligher ones towards the centres of panels, and even lighter ones in areas which would be particularly exposed to the sun. IN places, at the edge of panels, you can even see hints of the black base coat.
Thing is, over time, everybody develops his own technique. Experiment - ideally on somehting cheaper than a Tamiya Abrams - and find what works for you.
Above all, have fun, and don't obsess about it. After all, it's only a hobby, right?
Cute and cuddly, boys, cute and cuddly!