#1
I had no problem playing guitar and singing, but now that i want to play complex basslines and sing, i keep stumbling. Any tips?
#2
Man, I know exactly how you feel! So many people make it look so easy, and some say "There's nothing to it!" Most of us know that the opposite is true. I wish there was some secret method that I could provide to you that would make it a snap, but there simply is no such method.

The best way is through slow, constant, and careful repetition. By that, I mean you have to practice singing and playing. Start slow, with an easy rhythm and bass line that is the same melody as the song. We are talking about mind-numbingly boring songs that you remember from early childhood, so it won't be fun. After you get the hang of singing the same melody that you are playing, you can start working on singing a melody that is different from your bass line. It is largely a question of being able to play the bass part of the song without thinking about it, and just slowly progressing from there. The better you get at it, the more able you will become to sing a complex vocal over a complex bass line. Whether you will ever be able to replicate Geddy Lee singing over the unbelievably complicated and fast bass line in The Analog Kid is an open question, but with a lot of practice, hard work, and perseverance, you should become able to sing and play most things.

And do not think that right now, you are all alone. No less a master musician than B.B. King (Yes; I know he is a guitarist, but he is still great) has been playing for decades and he readily admits that he simply cannot play and sing at the same time. Watch his performances and you will see that when he sings, he does not play. King likes to say: "First I sing, and then Lucille sings!" So you are in truly great company.

Keep plugging away at it. You'll nail it eventually.
"Maybe this world is another planet's hell?" - Aldous Huxley
#3
Sing along with the songs away from the mic, you'll soon develop it
G&L L2500
Squier Affinity Jazz Bass 5
Ashdown RPM pre-amp
Ashdown Little Giant 1000
300 watt 15" powered cab
450 watt 15" powered sub bass cab
2x10 + horn
1x15x10 + horn
#4
Yeah, people like Paul M, Sting, Geddy, Squire etc amaze me with that
#5
Another approach is that you need to be able to do one without thinking about it. For me learning the bass line until I can literally play it in my sleep helps, because I don't have to think about what I'm playing and can focus on the vocals

The issue with playing bass and for that matter drums, and singing is that oft times the rhythm runs counter to the melody line, which makes it much harder to coordinate both actions at the same time.

Another trick is to learn the bass line and the "talk" the lyrics over the bass line, then move to actual singing.
#6
I started way back doing what were called Doowops in support of the main vocals so when Beatlemania broke out it was already there.
G&L L2500
Squier Affinity Jazz Bass 5
Ashdown RPM pre-amp
Ashdown Little Giant 1000
300 watt 15" powered cab
450 watt 15" powered sub bass cab
2x10 + horn
1x15x10 + horn
#7
What may also help is listening to how the vocal part and the bassline work together, ie which notes are sung/played at the same time and on which beat do they occur. On which lyric does the chord change? Start slowly. Tapping your foot may also help.

But yeah, I think it's a lot about being able to play and sing without needing to think about it. You just need to learn the song really well.
Quote by AlanHB
Just remember that there are no boring scales, just boring players.

Gear

Bach Stradivarius 37G
Charvel So Cal
Fender Dimension Bass
Hartke HyDrive 210c
Ibanez BL70
Laney VC30
Tokai TB48
Yamaha FG720S-12
Yamaha P115