Dash blockreward is as follows :

45% goes to miners
45% goes to masternodes
10% goes to Dash Decentralized budget

In order to run a Dash masternode you need to have accumulated 1000 Dash, which can be kept in a personal cold wallet somewhere
offline. That 1000 Dash serves as collateral to the network, which the Dash network can verify to determine if it is still intact.
Not only will the masternode get paid 45% of the blockreward for providing services to the network (services like Privatesend, Instantsend and its Decentralized Governance
and Budget system), it will also have a vote in Dash budget system.

link : https://dashpay.atlassian.net/wiki/display/DOC/Masternode+vs.+Mining
    
If you dont have 1000 Dash you can look for sharing that 1000 Dash with other people, so you can still accumulate some interest.
These are trusted solutions, meaning you have to rely on a third party

link : https://dashpay.atlassian.net/wiki/pages/viewpage.action?pageId=1867885

An untrusted solution (a decentralized solution with no third party in between) is in the planning for Dash Evolution, is called Masternode Shares and it will take time (estimate a year)

link : https://www.youtube.com/watch?v=N7T-a2xm5c0&index=9&t=263s&list=PLiFMZOlhgsYJPIiG0bjT1_SuT5h7NqPCC  

Here are the details of ROI that you can exspect from running 1 masternode :



link : https://dash-news.de/dashtv/#value=1000
(multiply the value if you want to calculate it for more masternodes)

Currently a masternode owner can exspect an annual interest of 9.34%
The costs for masternode owners will be the renting of their VPS server (in most cases that is about $5 per month) and they will need to keep their masternode always up to date and active.