Below is basically all you need and this is from my working BGP configuration. If you only have a single /21 this is all you need, otherwise add the additional blocks to the permit rules.
For the 2nd ISP, just add the bgp neighbor stuff again. Full tables will take a few minutes to load when the router first starts.
set policy prefix-list ASyoursasn-Out rule 10 action permit
set policy prefix-list ASyoursasn-Out rule 10 description 'ASyoursasn BGP Announce'
set policy prefix-list ASyoursasn-Out rule 10 prefix yourIP/21
set policy prefix-list ASyoursasn-Out rule 200 action deny
set policy prefix-list ASyoursasn-Out rule 200 description 'Do not announce any other route'
set policy prefix-list ASyoursasn-Out rule 200 le 32
set policy prefix-list ASyoursasn-Out rule 200 prefix 0.0.0.0/0
set policy prefix-list DEFAULT-ONLY rule 10 action permit
set policy prefix-list DEFAULT-ONLY rule 10 description Allow-Default-Route
set policy prefix-list DEFAULT-ONLY rule 10 prefix 0.0.0.0/0
set protocols bgp yoursasn neighbor yourispIP description 'YouriSP AS Neighbor'
set protocols bgp yoursasn neighbor yourispIP prefix-list export ASyoursasn-Out
set protocols bgp yoursasn neighbor yourispIP prefix-list import DEFAULT-ONLY
set protocols bgp yoursasn neighbor yourispIP remote-as yourispasn
set protocols bgp yoursasn neighbor yourispIP soft-reconfiguration inbound
set protocols bgp yoursasn neighbor yourispIP update-source yourispIPyourend
set protocols bgp yoursasn network yourIP/21
set protocols bgp yoursasn parameters log-neighbor-changes
set protocols ospf area 0.0.0.0 area-type normal
set protocols ospf area 0.0.0.0 network yourIP/21
set protocols ospf default-information originate always
set protocols ospf default-information originate metric 10
set protocols ospf default-information originate metric-type 2
set protocols ospf parameters abr-type cisco
set protocols static route yourIP/21 blackhole distance 254