Sounds like you need to work on your approaches and mindgames. I had this same problem and when I realized what I was doing wrong it was like a lightbulb went off over my head.
There are some concepts, techniques, and tactics that, alongside raw talent and experience, simply put a player on a higher level than others. Approaching an enemy is a sub-category of the all important 'spacing' concept that has to do with the way that a player moves in on and engages an enemy.
The key terms here to remember are 'options' and how to 'cover' those 'options'. When you approach an enemy player, both of you have a set of 'options' that refers to what actions the player can take. When two players collide, the one who has put more thought into using their own 'options' to deal with the enemies 'options' and correctly guesses which 'option' the enemy will take, that player is the one who profits from that engagement.
A specific example might make this simpler:
As Ike you want to approach Marth, who is standing there waiting for you. You start dashing at Marth and as you are about to come into his range it is now time to consider the 'options' both player has.
As Ike you have options like these:
A) Dash Attack, this option beats an enemy grab but fails against anything else.
B) Dash Grab, this option beats shields but fails against anything else.
C) Counter, this option beats an instant enemy attack but fails against anything else.
D) Shield and see what they do. This option will beat any non grab attack and also doesn't leave you open like counter does if the enemy doesn't fall for it.
Meanwhile Marth has options like these.
A) Use a jab, tilt, dancing blade, or smash (from least risky to most risky if the enemy shields).
B) Suddenly run forward and dash attack Ike before he gets in range to do anything.
C) Shield expecting an attack, then grab if correct.
D) Counter if he REALLY expects a dash attack, riskier than shielding but a higher payoff.
E) Shield Breaker if he expects the enemy to dash in and shield.
Each player has more options than those, especially when you get into aerials, but you get the idea. Each player has tools, each player has been paying attention to the other player and has an idea of what they expect. Every approach is a mindgame between two players, and if you just run in without thinking you're just going to get slaughtered unless the other player is similarly mindless in their play.
All in all, don't just use whatever approach option you WANT to use, look at how your opponent has been reacting and act based on that. If they shield grab you every time you run in then do a grab next time instead of a dash attack. If they smash attack you when you run in then run into a shield and punish them when they hit you you. If they roll towards you when they are at the edge, do a down smash as they are under you and send them flying. If they always jump when you get close then jump attack in the air before they get their and knock them out of the sky.
Smash really is a lot more of a strategy game then people seem to give it credit for. When two players are both aware of the options each has it becomes a completely different experience complete with psychological conditioning, bluffs and double bluffs, feints, false openings, positioning strategies relying on a centimeter, etc. I think most people will find smash to be a stimulating mental exercise once they get past the 'run at the other guy and hit my attack buttons' stage.
