For one thing, check out the
Yoshi subforum here, and try to learn some new tricks and skills that will help you along the way. See if there's any combos you didn't know about before, or maybe see what moves autocancel. Another thing you should do is LEARN FROM YOUR LOSSES. See why you are losing. Do you roll a lot? Are you not spot dodging right? Did you airdodge too late for not airdodge at all? The small things really count. Smash is a learning process, and you have to learn one thing at a time. For the first few days focus on this. Then start to focus on that. And keep it simple for right now. Don't worry too much about the advanced tech like perfect pivoting or jump canceled upsmashing. Learn the basics: defensive options, aerial mobility, spacing, set-ups, and reads.
Another tip I have for you, along with other people who are trying to get better is to pick up different characters. I originally played Ike exclusively, and he's an awesome character, but he isn't perfect. When I eventually picked up Falcon, I learned a lot more about grabs, grab follow ups, combos, etc. and my experience of playing with Ike and his spacing allowed me to play Falcon better. When I started playing Rosalina, I started to learn how to DI properly as she's such a light character and dies much faster, so it was more important for me to understand. Now when I go back to playing Ike, I can apply the other skills I've learned through the other characters and vice versa.
And personally, I think that it's better to play with people who are better than you, rather than people who are worse than you. It forces you to think creatively and in new ways. Up until about yesterday I was really confident with my Ike. I was winning a significant majority of For Glory matches, and beating several friends. I even made it to winners finals in a minor online tourney, so I was pretty proud of myself. Well recently I ended up playing @
san. If you don't know who San is, he was one of the best Ike mains in Brawl so naturally a lot of his skill transferred over to Sm4sh. On top of this he's been really active in the Ike Subforum helping all of us newbies understand the character and has been a leading force in the findings of Ike's metagame. To put it simply: he's really good. Well when we started playing this guy annihilated me. We probably played Ike Dittos for an hour, maybe more, and I didn't win a single game. But that's okay, because I understood how much better I can be with Ike. I saw him doing things I didn't know were possible. Yeah it sucks to lose, but it's awesome to know that it's possible to improve.
Moral of the story: get active in a community and play against people who will help you improve. If the Yoshi subforum has a Skype group, get involved in that. Add some people who are willing and play with them. And remember, it's okay to lose. Another great place to find Smashers is
http://smashladder.com/ Tons of people there always wanting to play. But it's great because you help each other grow, and in time you are better than a lot of other players so you can help them improve!
Just remember, it's a learning process and it's going to take time. But if you stay dedicated and actively make an effort to get better, you will.