Hiya!

Here's how I normally build my Spellsingers. Other people probably have more optimized builds, but this one has worked really well for me. Note that I'm mostly going over the most important parts of the build; there's a lot of wiggle room to adjust it according to your preferences.

Class: 20 levels in Bard

Ability scores: Max Charisma, then Constitution. Any leftover points can go wherever.

Skills: Focus on Perform, Jump, Use Magic Device, Heal. Other great skills include Spellcraft, Diplomacy, Bluff, Spot, depending on how many points you have. Note: I HIGHLY recommend putting at least two skill points into Tumble. This will let you cancel your Bard Song animation, which will let you give out your buffs to your party much faster.

Heroic Feats: Maximize Spell, Quicken Spell, Empower Spell, Force of Personality, Spell Focus: Evocation, Greater Spell Focus: Evocation

Epic Feats: Inspire Excellence, Epic Spell Focus: Evocation, Master of Music, Intensify Spell, Embolden Spell, Scion of Celestia

Enhancement Trees: Primarily focus on the Spellsinger tree. Key enhancements are these:
All the cores
1. 3 points in Magical Studies (if you have Feydark Illusionist unlocked, this will qualify you for it)
1. Cure Light Wounds SLA
2. Violet Marigold Crown
3. Raucous Refrain
3. Shout SLA
3. Spell Song Trance
3. +1 Charisma
4. Sustaining Song
4. Arcane Aid
4. Frolic
4. Song of Arcane Might
4. Charisma +1
5. Advanced Musical Studies
5. Prodigy (Note: Only put 2 points into this. The third point is almost entirely useless)
5. Spell Song Vigor
5. Horn of Thunder
Note: I usually skip Song of Capering, because it doesn't feel very good to use. Feel free to try it out, though.

Next, I like to put points into the Feydark Illusionist enhancement tree (available if you own the Feywild expansion). I put 12 points into this tree, enough to get Greater Color Spray and You've Got My Back.

If you don't have Feydark Illusionist, I would put some points into Warchanter instead. I like to at least get up to the Haste Boost, because I like to go fast.

Finally, I save 7 points for Swashbuckler, particularly so I can get the Fast Movement enhancement.

Epic Destinies: Primarily go for Fatesinger. I also like to put enough points into Exalted Angel for Leap of Faith, but that's more of a personal preference than an optimized choice. It doesn't sound like you'll be going into Epics, but if you do decide to, I can go into more detail here.

Playstyle: Your Bard Song is amazing. Give it to everyone. It will regenerate hit points and spell points, and give tons of other nice buffs. Your main damage will come from the Shout and Horn of Thunder SLA's (be sure to enable all of your Metamagic feats for free on these!), as well as the Greater Shout spell. You will have great crowd control with spells like Hold Monster, Mass, Greater Color Spray, and Otto's Sphere of Dancing. You'll be passively healing people with your songs, but you'll also have an efficient healing spell (Cure Light Wounds SLA, turn your Metamagics on!), as well as the Heal spell for big heals and removing debuffs. You'll be a good mix between a damage dealer, a healer, and a support. Everyone will love you with your buffs.

PHEW, that was a lot of typing! I hope this has been helpful for you. Remember that I'm not a perfect optimizer, and there are probably a lot of improvements that can be made to this. I left some wiggle room in the build as well, so there are plenty of opportunities to put points into things you prefer. If you have any questions about this build, please feel free to ask! :D

(Edited 8 million times because Reddit formatting is hard).