I’ve been spending a lot of time recently assembling standard parts and have got infuriated by parts disappearing off screen as I add relationships meaning I have to go hunting for them. Zooming in and out is time wasting and index finger exercise I could do without.
Using capture fit is a big help and this suggestion can be used in conjunction with it.
What I’ve started doing is using the connect relationship as the first relationship I apply.
What you do is choose a point on each part that you know will always be coincident. The two parts are then tied together and you can go ahead and apply the rest of the relationships without your parts flying off.
Notice also in this video that I use a floating planar relationship between the base plane of the new part and the existing part which allows me to align the new part to any parallel face.