What are the conditions of deliberate practice?
My causal impression is that the literature on deliberate practice is a little vague about how deliberate practice differs from other forms of practice.

I think it was Ericcson who distinguished between work, play, and deliberate practice. Work is to get something done, play is for enjoyment, and deliberate practice is activity completed with the goal of improving skill.

A few general features of deliberate practice include: 


It should be effortful and is likely to involve a degree of focus
The intensity and focus of deliberate practice may limit the amount of time that can be dedicated to it per day, and it is important to get appropriate rest either side.


Deliberate practice is generally designed to be at the optimal level of challenge given your current ability. It should also include feedback.

In general it is going to help a lot to have a tutor. Tutors go by many names: coaches, supervisors, mentors, trainers, teachers, and so on. The tutor can assist in providing you with appropriate exercises and giving you the right feedback. So for example, music instructor may push you to master specific exercises or get you to master a particular musical piece because they can see that it will challenge you. Similarly, a tennis coach may get you repeating particular strokes with feedback.

That said, if you don't have a tutor, you can still attempt to apply the principles of deliberate practice to your own learning. It's harder and probably less efficient, but it is possible to teach yourself a lot of things. A few general suggestions:


Be clear on the skill you're actually trying to master. What is the goal state? What would be evidence of you achieving that state? For example, in academia, evidence of achievement might be seen in getting some top-tier publications. In golf, it might be achieving a certain handicap.
Try to create learning environments where you get feedback on your performance. For example, when doing mathematics exercises you get feedback. When you submit journal articles you get feedback through peer review.
Reflect on whether the activities you are doing are actually improving your skill. Be mindful of when you are getting stuck in a rut. Explore learning materials that might be useful.


I'd also make a final point about the importance of actual work in acquiring a skill. The deliberate practice literature does have a tendency to emphasise the importance of drills and background study (e.g., practicing your serve; studying famous chess masters, etc.). However, in many cases, actually doing the activity (i.e., that which is called work) can be an incredibly valuable learning experience. I vaguely recall a study that looked at soccer referees that showed that number of matches refereed was an independent predictor of referee performance over and above deliberate practice.