There's some incorrect answers in this thread. Like all aspects of labour relations in the USSR, recruitment processes were often opaque and did not conform to stated policy or supposed ideology. Nonetheless, there were a few identifiable avenues of recruitment in the 1950s:

• Direct allocation. Directly placing people into jobs ceased to be a significant feature of the Soviet economy after the 1930s, by which time it had proven to be grossly inefficient and unreliable. (People aren't robots: despite increasing anti-labour legislation, many simply left jobs they didn't like.) By the 1950s there was relative freedom of movement between and into jobs. Graduates from vocational and specialised professional schools were expected to serve three to four years in assigned industries, after which they were free to move. Not only did this period not apply where graduates had already lined up a job, it also included time spent on national service, training, maternity leave etc. By the 1960s there was no legal force behind such allocations (ie people could reject their assignment with no legal consequences) and by the 1980s a decided minority of new recruits occupied allocated roles. And, naturally, there were illicit ways of avoiding this service.

• Organised recruitment. Another holdover from the 1930s, organised recruitment (orgnbor) was essentially an updated form of seasonal labour. It comprised recruiting peasant volunteers into certain industries (eg construction, logging) for an agreed contract length, typically two years. But this was never a major recruitment stream and had shrunk in importance by the late 1950s. Organised recruitment never lived up to the state's expectations.

• Labour market. The Soviet Union had a functioning labour market, albeit a distorted one. After the 1930s this was the primary source of labour for industry. Enterprises and ministries were free to recruit directly from the labour pool as needed. Given the tendency of Soviet managers to hoard labour, this was often and the market could be competitive. Advertisements, employment agencies (later) and economic/material incentives were all used to attract workers. This was by far the most typical way of recruiting into industry.

So the primary means of managing labour in the USSR remained the labour market. Far from simply slotting workers into jobs, Soviet planners spent a huge amount of time managing wage policy across the economy, to attract workers where needed; enterprise managers spent just as much time subverting such policies to retain their best staff. Post-Stalin any obligatory work was for a limited time and usually limited to vocational or specialised workers employed by an enterprise affiliated to their school.

On the matter of pay, there is again incorrect information here. Pay equalisation hadn't been state policy since the early 1930s, when Stalin came down hard against this. Wage scales in industry were based on skill grades and the product of negotiation between the planners, enterprise and local unions. Across sectors, wage differentials tended to be heavily skewed towards blue collar jobs but that's a bit of a false reading. Pay was absolutely not "a matter of being able to afford basic necessities like food and clothes": wages rose consistently (albeit slowly) and the state deliberately kept prices of consumer goods artificially low. What counted in the USSR was access, access to good housing, more and higher quality goods, non-subsidised services, patronage networks, etc. These provided incentives for workers/professionals.

The Soviet employment model was not a million miles removed from that of the West, possessing both a labour market and economic incentives. Both were heavily distorted from what we are used to - and existed in the opaque world of Soviet labour relations - but this was not a system simply allocating people roles like they were widgets. Outside of the forced labour system, 'administrative' allocation of labour was not a major feature of the Soviet system. A lesson in why it's rarely a good idea to take Soviet ideology or theory at face value.

Reading

Granick's Job Rights in the Soviet Union is old but provides a good summary chapter on Soviet recruitment avenues. Filtzer is my go-to man on how Soviet labour relations actually functioned, Soviet Workers and De-Stalinization being the relevant work for this period.