First and foremost...there are no 1-day hoppers availabe at TDR, so you would have to buy two separate tickets to do both parks.
Adventurer up above does have a point... TDS is worth a whole day visit because it's so so unique. But TDL is also a fabulous park to spend the day, and enjoy some nice versions of the classic rides we love (TDL's Splash and Hunny Hunt are grand and can't be missed, for example)
Here is my suggestion.... If you choose a slow day to visit (non-holiday, non-weekend) you may be able to follow one of these itineraries if you are willing to dish the money for tickets, and also if both parks are opened until 10pm.
Get a 1-day Pass for TDL. Show up before opening time and wait for park to open. As soon as you are in, go get FP for Astroblasters, then continue to Hunny Hunt and do standby.. As soon as it's time for another FP at another ride, get one. Continue to enjoy other things around the park such as the Disney Dreams on Parade and other rides. I personally like Big Thunder, Splash, Mickey Mouse Revue (very nostalgic attraction from WDW's opening day in 1971), Mystery Castle Tour. Other rides are similar to their counterparts in other DL parks...so skip Star Tours, Space Mountain, Pirates, Jungle Cruise and some of the dark rides in Fantasyland. If you can catch one of the stage shows...such as "One Man's Dream 2"...go for it.
Then... around 5:30pm, leave TDL. Hop on the TDR Line Monorail and head to TDS. Takes about 8 mins to travel from TDL to TDS. Once you arrive at TDS, buy the "After 6pm Passport". Enter TDS at 6pm (there may be a little line of 'After 6' ticket holders. As soon as you are inside the park, cross under the Miracosta and turn right and go around Mediterranean Harbour, Check the status of the stand by lines for JTTCOTE and 20K. If less than 20 mins, then go on them. After Mediterranean Harbor, head out to Arabian Coast, ride "Sindbad", then continue to Lost River Delta and ride Indy; then Port Discovery and ride "StormRider". Do "Aquatopia" if it's less than a few minutes wait.
If you are interested in catching "BraviSeamo!" over the main Lagoon, then head back to Mediterranean Harbor no later than 30 mins before show time. After "BraviSEAmo!", head back to Mermaid Lagoon and check it out. Cool place to so some carny rides at this time since it gets very slow. Or take time to explore American Waterfront and do shopping or eating before the park closes it's venues. Skip the fireworks over the park since they are not as good as "Believe" or "Wishes", and same show plays simultaneously for both TDS and TDL. Take advantage of your time and stay until closing time.
You will be exhausted but made the most out of your time and money invested in tickets.
Get to TDS early before opening time. Get a 1-day pass. As soon as you enter...go with the flow. Go straight to 20K and get FP, then go to JTTCOTE and stand by for it. After JTTCOTE, leave this area and head out to Lost River Delta and ride INDY. If you have time before your 20K FP time window, head to Port Discovery and ride "Stormrider". Then use your FP for 20K. From this time on..you can slow down a bit. Take in a show or explore Arabian Coast and ride "Sindbad", or Mermaid Lagoon and do go in and see the "Little Mermaid" show. Other shows worth watching are "Encore", "Sail Away", "Mystic Rhythms", and the daytime extravganza on the lagoon "Porto Paradiso Water carnival". Get lunch, shop or whatever... If you have been able to see JTTCOTE, 20K, Sindbad, Lil Mermaid show, INDY, Stormrider, one or two stage shows, do some shopping and/or lunch, and have had time to soak in all of the woderful themed architecture around the park, then you have had a pretty succesful day at TDS. Attractions that may be skipped are : Magic Lamp Theater, Aquatopia, all carny rides in Mermaid Lagoon, Trolley Tram between American Waterfront and Port Discovery, and Big City Vehicles.
At around 5:30 or so, you can hop on the TDR Line monorail and head to TDL. Travel time is like 6 mins.
Once you arrive at TDL, get the "After 6 Passport", enter the park try to find an attraction that may be manageable. By this time, ALL FP tickets at ALL rides, will be gone. I would concentrate on rides without FP so you can do as much as possible...some of these are the Mystery Castle tour, Jungle Cruise, Star Tours. If you are interested in watching "Dreamlights" Parade. Get a spot near the Haunted Mansion as this is where the parade starts. Any area in the vecinity of Haunted mansion, Dumbo, or Peter Pan would be ideal. As soon as the parade ends, head quickly across Fantasyland, past IASW and go into the Pooh Hunny Hunt stand by line. The line should not be too long since the rest of the park will be occupied watching "Dreamlights". Ride Hunny Hunt.
After this..assess the situation. Keep in mind Astroblaster is the same one as DL so it can be skipped. Fireworks go off at 8:30pm...and after that, the park may start to slow down. Choose the rides you want to see and wait them out until time runs out and park closes. This will be the best you could do at TDL if you choose to see TDS first thing in the day.
The decision is yours now. Choose the itinerary you feel would work best for you. But remember...these options work best when you choose to go to the parks on a day regular non-holiday weekday and when both parks are opened from 9am till 10pm.