I am a 1st level bard/4th level thief, do you have any Suggestions about spells, feats or general tips and tricks?

Depending on your charisma, if its low pick spells that dont have a save dc.  But without any other knowledge that's about all I can say.

Tips for a Bard 1/Rogue (Thief) 4:

• True Strike sucks in general, but using it on a turn when you aren't in position to make an attack so that you have advantage next round (and can thus get Sneak Attack) is probably its best possible use. Although I'd still suggest Mage Hand, Minor Illusion, Message, Light, or Friends as more useful for a thief-type character.
• Disguise Self, Charm Person, Distort Value, Feather Fall, and Silent Image all seem like good thief-y spells to take, but aren't useful in combat. For combat, I'd suggest Faerie Fire, Sleep, or Hideous Laughter as those can again set up your Sneak Attack. 
• If you're interested in out-of-combat versatility, more levels of Bard are great (Whispers if you want to be stabby, Glamour if you want to be talky, or Lore if you want to be flexible are the best three). If you're mostly interested in combat optimization, I'd suggest just sticking with Rogue to get more Sneak Attack and more feats as soon as possible.
• Defensive Duelist, Dual Wielder, Inspiring Leader, Lucky... all of those could be great feats for a thief. Skulker and Dungeon Delver may or may not be useful depending on how your DM runs things. Mobile is always nice for a melee Rogue that wants to dart in and out of combat.